My statement here does not help at all but....I totally despise not tracking basis, whatever the excuse maybe. I have had many of these including partnerships and S-Corps. I have a few companies that brought me on at the beginning of their business and all basis is tracked every single tax year. Matter of fact, one partnership bought out one of the partners and their were no questions or disputes over basis. My only suggestion is as you say, is to try to re-create the shareholder basis. I think we all go into this knowing the accuracy is just not there but like you and others, I have had to do the same. I like Abby Normal's suggestion using the balance sheet figures. But... who's to say those figure are a true representation of the equity accounts unless you can see every entry. At best this should be an accumulation of income and loss. However, it may be as you said, all you have. I would keep good notes on how I arrived at the shareholder basis. As far as your client/friend goes, just explain to him that is all you have to work with. Good luck with this and get some rest. It shows the person you are and the desire to do the right thing by your concerns. Again, get some rest my friend.