This study a) compared the effects of buprenorphine versus methadone maintenance on benzodiazepine and alcohol use and b) evaluated the prognostic significance of gender and psychopathology and their interaction with maintenance treatment. Eighty male and 36 female patients were randomly assigned to daily sublingual buprenorphine (4 or 12 mg) or oral methadone (20 or 65 mg). Maintenance medication was not associated with significant differences in alcohol or benzodiazepine use. Rates of abstinence from illicit opioids were significantly higher for females; within the buprenorphine 4-mg group, females also had significantly better retention, lower rates of opioid-positive urine samples, and higher rates of abstinence from illicit opioids. Lifetime sedative dependence was associated with significantly better retention, decreased rates of cocaine-positive urine samples, and increased rates of cocaine abstinence; among buprenorphine- but not methadone-maintained patients, it was also associated with increased rates of abstinence from illicit opioids.