Atypical antipsychotics offer advantages over earlier drugs for the treatment of schizophrenia, although few data exist on the relative merits of different atypical antipsychotics. A multicentre, double-blind, randomized trial was performed to compare amisulpride and olanzapine in the treatment of acute schizophrenia. Adult schizophrenic patients with dominant positive symptomatology received amisulpride (200-800 mg/day) or olanzapine (5-20 mg/day) for 6 months. The primary efficacy variable was change from baseline of the Brief Psychiatric Rating Scale (BPRS) score, assessed with a non-inferiority analysis. The evolution of positive and negative symptomatology, depression, social functioning and quality of life were assessed. Safety evaluation included adverse event reporting, neurological status and body weight. The improvement of BPRS score was 32.7% in the amisulpride group and 33.0% in the olanzapine group; thus, the efficacy of amisulpride was not inferior to that of olanzapine. All other secondary efficacy outcome variables evolved to a similar extent in both groups. Adverse event frequency was similar in both groups. Amenorrhoea was encountered only in the amisulpride group (6.2% of patients), whereas elevations of liver transaminases were more frequent in the olanzapine group (17% versus 3.7% of patients). The incidence and mean extent of clinically relevant weight gain were higher in the olanzapine group (35.1% and 3.9 kg) than in the amisulpride group (20.6% and 1.6 kg). The efficacy of amisulpride is not inferior to that of olanzapine in the treatment of acute schizophrenia. The side-effect profile of the two drugs differed.