I have a need to display a hierarchical select of a vocabulary as a series of radio buttons representing the top-level terms. When the user selects one of the radio buttons, the child taxonomy terms should be displayed below as checkboxes.

Do I need to build a custom AHAH form, or can I look at form altering the default hierarchical select widget?

2 Answers 2


For drupal 6 you may want to check out the module https://drupal.org/project/conditional_fields which basically lets you control which form elements depend on other form elements. It also has a handy GUI for doing this.

FYI drupal 7 has completely changed the game here and has implemented 'states api' - here is an example of what can easily be achieved - http://api.drupal.org/api/examples/form_example--form_example_states.inc/function/form_example_states_form/7


I managed to do something like that using Taxonomy Super Select (TSS) for Drupal 6. Here is a quote about it (from the module's project page):

... seamlessly overrides the select box generated by the taxonomy module and renders the terms based on if you are allowing multiple selections or not.


  • Multiple selection vocabularies show as checkboxes.
  • Single selection terms display as radio buttons.
  • Parent terms display as nested fieldsets
  • Option to display parented terms as form items
  • Ability to control which content types TSS will apply to
  • Works with all hierarchy configurations
  • Free tagging vocabularies are now supported.

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