I would definitely look to seem if filing was required for all years. If they are self employed, I DEFINITELY would file all 11 years.  If otherwise required due to income (look at gross, not net)  I would start at the oldest and move forward. If there are stock sales, there may be losses to carryforward. The statute of limitations is 3 years, but the clock doesn't start clicking on that until the return is filed. If there is tax due, then it will be due with penalties. If there are refunds, only the last 3 are recoverable, the older ones are lost, but the years now start their 3 year window to be audited. Get some good money from them up front.