BACKGROUND: Little is known about whether treatment in a specialised out-patient mood disorder clinic improves long-term prognosis for patients discharged from initial psychiatric hospital admissions for bipolar disorder. AIMS: To assess the effect of treatment in a specialised out-patient mood disorder clinic v. standard decentralised psychiatric treatment among patients discharged from one of their first three psychiatric hospital admissions for bipolar disorder. METHOD: Patients discharged from their first, second or third hospital admission with a single manic episode or bipolar disorder were randomised to treatment in a specialised out-patient mood disorder clinic or standard care (ClinicalTrials.gov: NCT00253071). The primary outcome measure was readmission to hospital, which was obtained from the Danish Psychiatric Central Register. RESULTS: A total of 158 patients with mania/bipolar disorder were included. The rate of readmission to hospital was significantly decreased for patients treated in the mood disorder clinic compared with standard treatment (unadjusted hazard ratio 0.60, 95% CI 0.37-0.97, P = 0.034). Patients treated in the mood disorder clinic more often used a mood stabiliser or an antipsychotic and satisfaction with treatment was more prevalent than among patients who received standard care. CONCLUSIONS: Treatment in a specialised mood disorder clinic early in the course of bipolar disorder substantially reduces readmission to a psychiatric hospital and increases satisfaction with care.