HOW DO I automatically add someone to a Usergroup based on a Profile field?

[ataraxia]

if ($userfield['field16']=='yes') // change this to suit you
		{
		   $user['usergroupid'] = 12;  // change this to suit you.
		}

Thanks, Amy

This looks close but I need to add the user to an "additional" usergroup, not as a primary one.

What code would you use to add a user to an additional (secondary) group. (the user may also belong to several other additional groups.)

Thanks