This case study describes the use of a daily raffle to increase attendance in a socialization center for approximately 75 adults diagnosed with mental illness. Specifically, the relationship between signing in, which was a measure of attendance, and the odds of winning points which could be exchanged for tangible and edible items was examined. An ABACADABACAD reversal design was used to evaluate the effects of three levels of odds (25%, 50%, 75%) on signing in to the center. Results indicated that signing in increased by 14% over baseline when the raffle was in place. However, no difference between the odds conditions was evident. A cost-benefit analysis showed that the raffle was cost effective for the center.