The participants were all admitted to treatment before July 1979 and were ages 20 and 40 years at some stage during their treatment. The relative risks of death in and out of methadone maintenance were calculated for those ages 20-29 and those ages 30-39. Results revealed that heroin addicts in both age groups were one-fourth as likely to die while receiving methadone maintenance as addicts not in treatment. This difference occurred because those in methadone maintenance were significantly less likely to die by heroin overdose or suicide while in maintenance. However, methadone maintenance had no measurable effect on the risk of death through nonheroin overdose, violence or trauma, or natural causes. A meta-analysis revealed that the reduction in overall mortality was consistent with the results of cohort studies conducted in the United States, Sweden, and Germany. The combined results of these five studies also indicated that methadone maintenance reduced addicts' risk of death to a quarter. Tables, figures, author photographs and biographies, and 49 references (Author abstract modified)