Use drupal #states to check a radio
You can use the form_api #after_build property to set a callback where you can manipulate the individual radio button elements (not the grouped "radios" element).

function your_form(&amp;$form, $form_state) {
  $form['radios1'] = array(
    '#type' =&gt; 'radios',
    '#title' =&gt; 'Radios 1',
    '#options' =&gt; array(
      0 =&gt; 'zero',
      1 =&gt; 'one',
    )
  );

  $form['radios2'] = array(
    '#type' =&gt; 'radios',
    '#title' =&gt; 'Radios 2',
    '#options' =&gt; array(
      0 =&gt; 'zero',
      1 =&gt; 'one',
    )
  );

  $form['#after_build'] = array('your_form_after_build_function');

  return $form;
}

function your_form_after_build_function($form) {
  $form['radios1'][0]['#states'] = array(
    'checked' =&gt; array(
      ':input[name="radios2"]' =&gt; array('value' =&gt; 1),
    ),
  );

  $form['radios1'][1]['#states'] = array(
    'checked' =&gt; array(
      ':input[name="radios2"]' =&gt; array('value' =&gt; 0),
    ),
  );

  $form['radios2'][0]['#states'] = array(
    'checked' =&gt; array(
      ':input[name="radios1"]' =&gt; array('value' =&gt; 1),
    ),
  );

  $form['radios2'][1]['#states'] = array(
    'checked' =&gt; array(
      ':input[name="radios1"]' =&gt; array('value' =&gt; 0),
    ),
  );

  return $form;
}