The aim of this study was to identify predictors of treatment success and of relapse, 1 and 6 months after inpatient opiate detoxification in an 8-bed unit in Geneva. Of all 73 patients admitted between June 1994 and June 1995, a majority (73%) successfully finished opiate detoxification. Detoxification was performed mainly with methadone tapering; the average duration of hospitalisation was 15 days. Factors associated with treatment failure were: cocaine abuse, presence of legal problems, and short duration of hospital stay. After 1 month, 65% of the patients were using drugs (half of them were dependent again, half of them had used occasionally) and 35% were completely abstinent (21% when excluding those in residential treatment). Predictors of rapid relapse were cocaine abuse and little concern with own psychological situation at baseline. After 6 months, 50% were physically dependent again, 13% had lapsed occasionally, 37% were abstinent (28% when excluding those in residential treatment). Only high benzodiazepine use at baseline was associated with medium term abstinence. Addiction severity index composite scores had considerably improved between baseline and 6 months. Prevention of relapse to opiate use after inpatient detoxification, especially for those with a concurrent cocaine abuse, should be improved.