I have an inventory accounting/reconciliation question.?

I've been on a few interviews and this question has been asked a few times now and I don't think I have a good handle on it yet? I've been a FInance Manager for years but inventory wasn't one of my strengths so I'm hoping someone could give me a quick answer - just so I know what to say. The question: The inventory in the sytem (book inventory) and the general ledger show a significant variance. Aside from taking a physical inventory and confirming the gl balance, what things do you do? Thanks very much.