use Symfony\Component\Validator\Constraints\True; // in your buildForm() method: $builder ->add("firstName", "text") ->add("lastName", "text") ->add("emailAddress", "email") ->add("t_and_c", "checkbox", array( "mapped" => false, "constraints" => new True(array( "message" => "Please accept the Terms and conditions in order to register") ), ) );

http://l3l0.eu/lang/en/2012/07/custom-advanced-symfony-2-form-type/