We described characteristics of subjects with benzodiazepine dependence that was typically complicated by harmful and hazardous alcohol use or high benzodiazepine doses, and assessed predictors of successful discontinuation of benzodiazepines for this group. Seventy-six patients who participated in a randomized clinical trial of two different gradual withdrawal treatment approaches were assessed. The trial was conducted between February 1995 and July 1999. The mean age +/- SD of subjects was 40.0 +/- 9.6 years, 55% were male, 38% were married or cohabiting, and 70% had received more than nine years of education. The median benzodiazepine dose was 35 mg/day (range 2.5-180) in diazepam equivalents. The median duration of benzodiazepine use was 84 (range 8-360) months. Subjects with lower benzodiazepine doses and no previous withdrawal attempts were more successful at benzodiazepine discontinuation. Cluster B personality/borderline personality disorder was associated with an inability to stop benzodiazepine use and with "dropping out" of treatment. Alcohol use-related disorders or other psychiatric diagnoses were not associated with outcome. Further studies on predictors of successful benzodiazepine discontinuation in different populations are required. Patients manifesting cluster B personality/borderline personality disorder and benzodiazepine dependence may need concomitant treatment for their personality disorders to benefit from benzodiazepine discontinuation treatment.