>>Hi,
>>
>>I've got a SQL Server Express 2008 R2 database which has a Person table where I store People and their dependents like this:
>>
>>PersonId
>>Name
>>ParentId
>>
>>So one PersonID can have many dependents by storing their ID in the ParentID field (simple self join).
>>
>>I want to set up referential Integrity on this table so that if a parent is deleted, their dependents are deleted (cascade). I created a database diagram, dropped my Person table on it and then dragged the PersonId field to the ParentID field. However, when I try to set the Delete Rule to Cascade, it is disabled.
>>
>>How can I do this?\
>
>I don't believe such complex RI is supported. Most likely you need to implement this RI through the trigger.

It is supported. My first guess is you set the relation the wrong way (wrong table has the FK field). I'll verify in a few minutes. Also make sure your primary key is set to PersonID in the Person table.