diff --git a/lib/nested_form/builder_mixin.rb b/lib/nested_form/builder_mixin.rb
index b572cf07..98331c7c 100644
--- a/lib/nested_form/builder_mixin.rb
+++ b/lib/nested_form/builder_mixin.rb
@@ -1,3 +1,5 @@
+require 'nested_form/unresolved_length_validator'
+
 module NestedForm
   module BuilderMixin
     # Adds a link to insert a new associated records. The first argument is the name of the link, the second is the name of the association.
@@ -31,6 +33,24 @@ def link_to_add(*args, &block)
 
       options[:class] = [options[:class], "add_nested_fields"].compact.join(" ")
       options["data-association"] = association
+      if Rails.application.config.nested_form.use_length_validators || options[:check_maximum] || options[:maximum]
+        unless maximum = options.delete(:maximum)
+          validators = self.object.class.validators_on(association)
+          length_validators = validators.select {|item| item.is_a? ActiveModel::Validations::LengthValidator}
+          if length_validators.length == 1
+            maximum = length_validators[0].options[:maximum]
+          end    
+        end
+
+        force_check_maximum = options.delete :check_maximum
+
+        if maximum
+          options["data-maximum"] = maximum
+        elsif force_check_maximum
+          raise UnresolvedLengthValidator, "nested form builder could not find length of #{association}"
+        end
+      end
+      
       options["data-blueprint-id"] = fields_blueprint_id = fields_blueprint_id_for(association)
       args << (options.delete(:href) || "javascript:void(0)")
       args << options
diff --git a/lib/nested_form/engine.rb b/lib/nested_form/engine.rb
index ba14a1f1..48603fd8 100644
--- a/lib/nested_form/engine.rb
+++ b/lib/nested_form/engine.rb
@@ -11,4 +11,11 @@ class ActionView::Base
       end
     end
   end
+
+  class Railtie < Rails::Railtie
+    config.nested_form = ActiveSupport::OrderedOptions.new
+    #set to true for global use of length validators to hide and show
+    #add and remove buttons
+    config.nested_form.use_length_validators = false
+  end
 end
diff --git a/lib/nested_form/unresolved_length_validator.rb b/lib/nested_form/unresolved_length_validator.rb
new file mode 100644
index 00000000..4e372d3e
--- /dev/null
+++ b/lib/nested_form/unresolved_length_validator.rb
@@ -0,0 +1,4 @@
+module NestedForm
+  class UnresolvedLengthValidatorError < StandardError
+  end
+end
diff --git a/vendor/assets/javascripts/jquery_nested_form.js b/vendor/assets/javascripts/jquery_nested_form.js
index dcdbc8ac..5b63c757 100644
--- a/vendor/assets/javascripts/jquery_nested_form.js
+++ b/vendor/assets/javascripts/jquery_nested_form.js
@@ -14,7 +14,7 @@
 
       // Make the context correct by replacing <parents> with the generated ID
       // of each of the parent objects
-      var context = ($(link).closest('.fields').closestChild('input, textarea, select').eq(0).attr('name') || '').replace(new RegExp('\[[a-z_]+\]$'), '');
+      var context = ($(link).closest('.fields').closestChild('[name]').eq(0).attr('name') || '').replace(new RegExp('\[[a-z_]+\]$'), '');
 
       // context will be something like this for a brand new form:
       // project[tasks_attributes][1255929127459][assignments_attributes][1255929128105]
@@ -43,6 +43,8 @@
       content     = $.trim(content.replace(regexp, new_id));
 
       var field = this.insertFields(content, assoc, link);
+      checkMaximum();
+
       // bubble up event upto document (through form)
       field
         .trigger({ type: 'nested:fieldAdded', field: field })
@@ -69,6 +71,8 @@
       
       var field = $link.closest('.fields');
       field.hide();
+
+      checkMaximum();
       
       field
         .trigger({ type: 'nested:fieldRemoved', field: field })
@@ -81,6 +85,21 @@
   $(document)
     .delegate('form a.add_nested_fields',    'click', nestedFormEvents.addFields)
     .delegate('form a.remove_nested_fields', 'click', nestedFormEvents.removeFields);
+
+  // if maximum is set for this nested
+  function checkMaximum() {
+    $('form a.add_nested_fields').each(function(){
+      var maximum = $(this).data('maximum');                // Maximum # of children
+      if(maximum != null) {
+        var assoc   = $(this).data('association');            // Name of child
+        var fields_selector = "div.fields :has(input[name*='["+ assoc +"_attributes]']):visible";
+        fields = $(this).siblings(fields_selector)
+        fields.length >= maximum ? $(this).hide() : $(this).show();
+      }
+    });
+  }
+  
+  checkMaximum();
 })(jQuery);
 
 // http://plugins.jquery.com/project/closestChild
diff --git a/vendor/assets/javascripts/prototype_nested_form.js b/vendor/assets/javascripts/prototype_nested_form.js
index 8a63e38d..e520f717 100644
--- a/vendor/assets/javascripts/prototype_nested_form.js
+++ b/vendor/assets/javascripts/prototype_nested_form.js
@@ -1,63 +1,90 @@
-document.observe('click', function(e, el) {
-  if (el = e.findElement('form a.add_nested_fields')) {
-    // Setup
-    var assoc     = el.readAttribute('data-association');      // Name of child
-    var target    = el.readAttribute('data-target');
-    var blueprint = $(el.readAttribute('data-blueprint-id'));
-    var content   = blueprint.readAttribute('data-blueprint'); // Fields template
-
-    // Make the context correct by replacing <parents> with the generated ID
-    // of each of the parent objects
-    var context = (el.getOffsetParent('.fields').firstDescendant().readAttribute('name') || '').replace(new RegExp('\[[a-z_]+\]$'), '');
-
-    // context will be something like this for a brand new form:
-    // project[tasks_attributes][1255929127459][assignments_attributes][1255929128105]
-    // or for an edit form:
-    // project[tasks_attributes][0][assignments_attributes][1]
-    if(context) {
-      var parent_names = context.match(/[a-z_]+_attributes(?=\]\[(new_)?\d+\])/g) || [];
-      var parent_ids   = context.match(/[0-9]+/g) || [];
-
-      for(i = 0; i < parent_names.length; i++) {
-        if(parent_ids[i]) {
-          content = content.replace(
-            new RegExp('(_' + parent_names[i] + ')_.+?_', 'g'),
-            '$1_' + parent_ids[i] + '_');
-
-          content = content.replace(
-            new RegExp('(\\[' + parent_names[i] + '\\])\\[.+?\\]', 'g'),
-            '$1[' + parent_ids[i] + ']');
+(function() {
+  //equivalent to addFields
+  document.observe('click', function(e, el) {
+    if (el = e.findElement('form a.add_nested_fields')) {
+      // Setup
+      var assoc     = el.readAttribute('data-association');      // Name of child
+      var target    = el.readAttribute('data-target');
+      var blueprint = $(el.readAttribute('data-blueprint-id'));
+      var content   = blueprint.readAttribute('data-blueprint'); // Fields template
+
+      // Make the context correct by replacing <parents> with the generated ID
+      // of each of the parent objects
+      var context = (el.getOffsetParent('.fields').firstDescendant().readAttribute('name') || '').replace(new RegExp('\[[a-z_]+\]$'), '');
+
+      // context will be something like this for a brand new form:
+      // project[tasks_attributes][1255929127459][assignments_attributes][1255929128105]
+      // or for an edit form:
+      // project[tasks_attributes][0][assignments_attributes][1]
+      if(context) {
+        var parent_names = context.match(/[a-z_]+_attributes(?=\]\[(new_)?\d+\])/g) || [];
+        var parent_ids   = context.match(/[0-9]+/g) || [];
+
+        for(i = 0; i < parent_names.length; i++) {
+          if(parent_ids[i]) {
+            content = content.replace(
+              new RegExp('(_' + parent_names[i] + ')_.+?_', 'g'),
+              '$1_' + parent_ids[i] + '_');
+
+            content = content.replace(
+              new RegExp('(\\[' + parent_names[i] + '\\])\\[.+?\\]', 'g'),
+              '$1[' + parent_ids[i] + ']');
+          }
         }
       }
-    }
 
-    // Make a unique ID for the new child
-    var regexp  = new RegExp('new_' + assoc, 'g');
-    var new_id  = new Date().getTime();
-    content     = content.replace(regexp, new_id);
+      // Make a unique ID for the new child
+      var regexp  = new RegExp('new_' + assoc, 'g');
+      var new_id  = new Date().getTime();
+      content     = content.replace(regexp, new_id);
 
-    var field;
-    if (target) {
-      field = $$(target)[0].insert(content);
-    } else {
-      field = el.insert({ before: content });
+      checkMaximum();
+   
+      var field;
+      if (target) {
+        field = $$(target)[0].insert(content);
+      } else {
+        field = el.insert({ before: content });
+      }
+      field.fire('nested:fieldAdded', {field: field});
+      field.fire('nested:fieldAdded:' + assoc, {field: field});
+      return false;
     }
-    field.fire('nested:fieldAdded', {field: field});
-    field.fire('nested:fieldAdded:' + assoc, {field: field});
-    return false;
-  }
-});
-
-document.observe('click', function(e, el) {
-  if (el = e.findElement('form a.remove_nested_fields')) {
-    var hidden_field = el.previous(0),
-        assoc = el.readAttribute('data-association'); // Name of child to be removed
-    if(hidden_field) {
-      hidden_field.value = '1';
+  });
+
+  //equivalent to removeFields
+  document.observe('click', function(e, el) {
+    if (el = e.findElement('form a.remove_nested_fields')) {
+      var hidden_field = el.previous(0),
+          assoc = el.readAttribute('data-association'); // Name of child to be removed
+      if(hidden_field) {
+        hidden_field.value = '1';
+      }
+
+      checkMaximum();
+
+      var field = el.up('.fields').hide();
+      field.fire('nested:fieldRemoved', {field: field});
+      field.fire('nested:fieldRemoved:' + assoc, {field: field});
+      return false;
     }
-    var field = el.up('.fields').hide();
-    field.fire('nested:fieldRemoved', {field: field});
-    field.fire('nested:fieldRemoved:' + assoc, {field: field});
-    return false;
+  });
+
+  function checkMaximum() { 
+    var add_buttons = $$('form a.add_nested_fields');
+    for(var i = 0; i < add_buttons.length; i++) {
+      var el = add_buttons[i];
+      var maximum = el.readAttribute('data-maximum');                // Maximum # of children
+      if(maximum != null) {
+        var assoc   = el.readAttribute('data-association');
+        var fields_selector = "div.fields :has(input[name*='["+ assoc +"_attributes]']):visible";
+        var fields = el.siblings().filter(function(sibling) { 
+          return sibling.match(fields_selector);
+        });
+        fields.length >= maximum ? el.hide() : el.show();
+      }
+    };
   }
-});
+
+  document.observe('dom:loaded', checkMaximum);
+})();