BACKGROUND The value of family psychoeducation for schizophrenia has been well established, and indications for its use have recently expanded to include bipolar affective disorder. However, no study to date has adequately examined its use in depression. OBJECTIVE To examine family psychoeducation in the maintenance treatment of depression and to investigate the influence of the family's expressed emotion (EE) on its effectiveness. METHODS Of 103 patients diagnosed with major depression and their primary family members, 57 pairs provided written informed consent. The pairs were randomly allocated to the intervention (n = 25) or control (n = 32). One family in the intervention group and two in the control group withdrew their consent after randomisation. The intervention group underwent four psychoeducation sessions consisting of didactic lectures about depression and group problem-solving focusing on how to cope in high-EE situations. Patients did not attend these sessions. Patients in both the intervention and control groups received treatment as usual. The families' EE levels were evaluated through Five-Minute Speech Samples. The primary outcome was relapse. RESULTS Time to relapse was statistically significantly longer in the psychoeducation group than in the control group (Kaplan-Meier survival analysis, P = 0.002). The relapse rates up to the 9-month follow-up were 8% and 50% respectively (risk ratio 0.17, 95% CI 0.04-0.66; number needed to treat 2.4, 95% CI 1.6-4.9). In Cox proportional hazard analysis, baseline EE did not moderate the effectiveness of the intervention. CONCLUSIONS Family psychoeducation is effective in the prevention of relapse in adult patients with major depression.