Lookup on itself

I am trying to do a lookup on itself. The concept is that I have clients and some of those clients have sub-clients. Sometimes we work for the client and sometimes we work for the sub-client. I would ideally have a single table called clients and give the ability to have them optionally noted as a sub-client with the lookup relating back to its own record set.

I know this is doable in Sharepoint.

Help would be great.