Abstract Introduction and Aims Women are underrepresented in long‐term studies of alcohol dependence. While gender differences in drinking behaviour have been observed when starting treatment, very few studies have investigated gender differences in long‐term drinking outcomes. This paper evaluates gender differences in the long‐term outcome of patients treated for alcohol dependence. Design and Methods A cohort of 850 outpatients (19% women, age 39 ± 9 years) treated for alcohol dependence in specialist centres of C atalonia ( S pain) were followed up prospectively for 20 years. Covariance analysis was used to assess gender differences at 1, 5, 10 and 20 years in drinking behaviour, psychosocial stress and social functioning ( A xes 4 and 5 of D iagnostic and S tatistical M anual of M ental D isorders, T hird E dition, R evised). We evaluated gender differences in drinking trajectories using a multilevel model controlling for basal differences. Results Women started treatment earlier in their drinking career, with more symptoms of dependence. In the first year they remained in treatment longer and had more clinic visits. Women presented lower alcohol consumption than men at baseline, 5 and 10 years, and similar levels of stress and psychosocial functioning. When basal alcohol consumption, length of treatment and employment were controlled, female gender predicted less drinking at year 1 and a drinking trajectory closer to abstinence between 1 and 20 years. Discussion and Conclusions Increased severity of alcohol dependence in women starting treatment was not associated with a worse prognosis. Women did better while under treatment and achieved a better long‐term drinking outcome. Gender differences were not relevant concerning psychosocial stress and social functioning. [Fabián Bravo, Antoni Gual, Anna Lligoña, Joan Colom. Gender differences in the long‐term outcome of alcohol dependence treatments: An analysis of twenty‐year prospective follow up. Drug Alcohol Rev 2013;32:381–388]