The authors present a model for incorporating multifamily therapy in the treatment of chemical dependency and investigate the association of family participation in multifamily therapy group with treatment retention in a sample of 164 alcohol- and/or cocaine-dependent outpatients. Results indicate that level of family attendance at a multifamily group strongly predicted completion of short-term and long-term out-patient treatment. Effects were greater for cocaine-dependent than for alcohol-dependent subjects in analyses of short-term treatment retention. Multifamily therapy may be a powerful method to engage patients families in treatment and promote treatment retention, especially in the early, intensive phases of treatment for cocaine dependency.