Background: About 50 % of adult alcoholic patients relapse within 3 months of treatment. Previous studies have suggested that acamprosate may help to prevent such relapse. The aim of our study was to assess the efficacy and safety of long-term acamprosate treatment in alcohol dependence of adolescents. Methods: In this, double-blind, placebo-controlled study, we recruited 26 patients, aged 16–19 years, with chronic or episodic alcohol dependence. Patients were randomly allocated treatment with acamprosate (1332 mg daily) or placebo for 90 days. Patients were assessed on the day treatment started and on days 30, and 90 by interview, self report, questionnaire, and laboratory screening. Findings: 13 acamprosate-treated and 13 placebo-treated patients completed the treatment phase: of those withdrawn, 11 (1 vs 6) relapsed, 5 (3 vs 2) refused to continue treatment, 3 (1 vs 2) had concurrent illness, and 2 (1 vs 1) had adverse side-effects. At the end of treatment, 7 acamprosate treated and 2 placebo-treated patients had been continuously abstinent (p = 0.0076). Mean cumulative abstinence duration was significantly greater in the acamprosate group than in the placebo group (79.8 [SD 37.5] vs 32.8 [19.0] days; p = 0.012). Interpretation: Acamprosate is an effective and well-tolerated pharmacological adjunct to psychosocial treatment programmes.