A large percentage of individuals are dually-diagnosed with a psychiatric disorder and a substance use disorder. Such persons typically face more difficulties and have poorer outcomes than do single disorder substance users. Among noncomorbid substance users, treatment and participation in 12-Step groups have been shown to enhance the likelihood of abstinence from substance misuse. Specialized 12-Step based fellowships have recently emerged to address the recovery needs of dually-diagnosed persons. The present study is a longitudinal investigation of the effect of such 12-Step based groups on abstinence among dually-diagnosed persons. Participants were members of Double Trouble in Recovery (DTR) who were recruited at community-based meetings in New York City and reinterviewed twice at yearly intervals. Generalized estimating equation analysis indicated that, over the two-year study period, ongoing DTR attendance was significantly associated with a greater likelihood of abstinence after controlling for other pertinent variables, such as mental health symptoms. For clinicians, these findings underline the importance of fostering stable affiliation with specialized 12-Step based groups among their clients.