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Loan to son - how to get it back
As per JohnFx's comment above, consider whether it's worth more to you to just write this off. If not, if you feel that your son will be able to consider this without taking it personally, or you're willing to risk that relationship, then talk to him about it. Lay out the reasons why you need the money. If there are other children, it might be a simple matter of fairness to them. Based on your idea of deducting the money from his inheritance, I assume that the value you're docking from his inheritance will go somewhere else. Offer alternatives. You say that you can't take any money from him now, but letting him know that he can pay you in the future in lieu of loss of inheritance might be worthwhile. Be prepared with an idea of what to suggest if he says he can pay you some amount of money. Figure out what might be an acceptable payment plan and how to handle it if, at some point, he can't make payments for a time. This is a potentially ugly situation, and I can't guarantee that it will turn out better, but the more you prepare for the questions he's going to ask, the better off you're going to be.