This study describes a contingency management intervention applied in group treatment. In an HIV drop-in center, groups were held on Tuesdays and Thursdays for 35 weeks. An ABB'CA design was used, in which reinforcers were available in non-A phases. In the initial B phase, reinforcers were available only on Tuesdays, and they switched to Thursdays in the B' and C phases. The reinforcer was a drawing that was associated with the possibility of winning a prize. Reinforcers were provided for attending group and completing steps related to treatment goals. The number of drawings escalated with weeks of consecutive attendance and activity completion in the B phases; in the C phase, a fixed number of draws were provided. Overall, the procedure increased attendance, with an average of 0.7 clients (range 0-4) per session in the initial baseline phase to an average of seven clients (range 2-12) during reinforcement phases. The percentage of activities completed also rose from 25% during baseline to 65% during reinforcement phases. These data suggest the feasibility of a group-based contingency management intervention.