Elderly psychiatric patients often present with psychotic symptoms that need antipsychotic treatment. Olanzapine is one of the atypical antipsychotics with efficacy for psychotic symptoms and a safer side-effect profile than typical antipsychotics. This study was conducted to assess the efficacy and safety of olanzapine for treatment of geriatric psychosis. The sample population comprised 94 acute-ward patients who were 65 years of age or older. Clinical assessment was conducted at baseline and also at 4 weeks after commencement of olanzapine treatment, with use of the Brief Psychiatric Rating Scale (BPRS) and Clinical Global Impression Improvement (CGI-I) instruments. A 4-week therapeutic evaluation was completed for 80 patients, 73 of whom (91.3%) experienced mild to substantial improvement as determined from the CGI-I. A mean 52.6% reduction from baseline was also determined from the BPRS. The mean daily dosage of olanzapine in the fourth week was 10.1 +/- 5.3 mg/d (range, 2.5-20.0). Higher olanzapine dosages were administered for patients with functional psychoses than for an analogous group with organic mental disorders. Adverse effects were monitored for all 94 patients, the most common of which were somnolence (18.1%), dizziness (18.1%), and weakness of legs or bradykinesia (16.0%). Body weight and fasting triglyceride and sugar levels were significantly elevated after olanzapine treatment (2.2, 39.9, and 8.9% from baseline, respectively). It seems reasonable to suggest that olanzapine is efficacious for geriatric patients with psychosis and that the dosage should be diagnosis-dependent.