OBJECTIVES. This study evaluated the influence of age, gender, vending machine lockout devices, and tobacco industry-sponsored voluntary compliance programs ("It's the Law" programs) on underage youths' ability to purchase tobacco. METHODS. Twelve youths made 480 attempts to purchase tobacco in Massachusetts from over-the-counter retailers and vending machines with and without remote control lockout devices. Half the vendors were participating in It's the Law programs. RESULTS. In communities with no requirements for lockout devices, illegal sales were far more likely from vending machines than from over-the-counter sources (odds ratio [OR] = 5.9, 95% confidence interval [CI] = 3.3, 10.3). Locks on vending machines made them equivalent to over-the-counter sources in terms of illegal sales to youths. Vendors participating in It's the Law programs were as likely to make illegal sales as nonparticipants (OR = 0.87, 95% CI = 0.57, 1.35). Girls and youths 16 years of age and older were more successful at purchasing tobacco. CONCLUSIONS. The It's the Law programs are ineffective in preventing illegal sales. While locks made vending machines equivalent to over-the-counter sources in their compliance with the law, they are not a substitute for law enforcement.