The IRS gets reports from 3rd parties regarding income paid to specific people. If you’re living on your investments, and making money off of interest, dividends, pensions etc. it will be reported. Likewise, some sorts of government benefits are considered taxable income i.e., social security and unemployment comp. But if you don’t’ have any reported taxable income, IRS is unlikely to care unless you otherwise come to their attention, i.e., Al Capone. I didn’t file taxes during the time I was in law school and for a year afterward, because I didn’t have any income. IRS didn’t care. Unless they got some reason to think that you may have to file taxes, i.e., significant reported income, or a ‘lifesytle’ problem, they aren’t going to question it under normal circumstances. Social Security is non-taxable, UNLESS the person’s other, taxable, income exceeds certain amounts, and even then is only partially taxable. For 2009, the first $2,400.00 of unemployment comp is not taxed by the federal government. The point is, the money had to come from somewhere, and Section 61 taxes income ‘from whatever source derived’. So you need to ask those questions above, and satisfy that they had no INCOME for those three years. If they had no income, or if their actual income was less than the exemption and standard deduction amounts for those years, or their income was non-taxable for another reason, then yes, it’s possible for them to not have filed for three years, and not be required to file (especially in the case of taxable income < exemption + standard deduction, a situation you frequently see in the elderly who live strictly off of social security). If someone else was supporting them, were they claimed as a dependant? If they were not, they should have been, unless they don’t meet the requirements. Also look at barters, which are taxable at the FMV of the good/service provided. Once you’ve satisfied all that, then yes, it is possible, though the IRS may – may – send a letter asking about the intervening years. This will be especially true if the client has gotten forms which are also provided to the government (W2, 1099, 1098 (interest), etc.) and the client has not filed a return. To answer your question directly: just because you’re not ‘working’ does NOT mean you don’t file taxes.