OBJECTIVE: Evaluate the doses of olanzapine, risperidone, and haloperidol in outpatients with schizophrenia. METHODS: A 6-month, prospective, comparative, study. Data were collected by psychiatrists at mental health centers and other outpatient facilities. The antipsychotic drug, doses, adverse events, CGI scale scores, and the GAF scale scores were recorded. Clinical response was defined as a decrease of at least 2 points on the CGI, with a final CGI score ? 4. RESULTS: 2,657 patients were included in this analysis. Initial and overall mean daily doses were 12.2 and 13 mg for olanzapine, 5.2 and 5.4 mg for risperidone, and 13.9 and 13.6 mg for haloperidol. Median daily doses were 10 mg for olanzapine, 6 mg for risperidone, and 10 mg for haloperidol. Significantly (p?0.001) lower proportion of olanzapine-treated patients (36.9%) experienced EPS than risperidone (49.6%) and haloperidol (76.0%) patients. Significantly (p?0.001) lower proportion of olanzapine-treated patients (47.8%) experienced any adverse event than risperidone (57.2%) and haloperidol (79.8%) patients. Significantly (p<0.05) greater proportion of olanzapine-treated patients (37.3%) were responders than risperidone patients (31.5%). Patients who had an initial CGI ? 5 had significantly (p<0.001) higher overall mean daily doses than patients with an initial CGI <5 Significantly (p<0.001) lower proportion of olanzapine-treated patients (10.2%) were receiving concomitant anticholinergic medication at the end of the study than risperidone (19.9%) and haloperidol (44%) patients. Significantly (p<0.001) lower proportion of olanzapine-treated patients (18.4%) were receiving other antipsychotics at the end of the study than risperidone patients (25.6%). CONCLUSION: Mean daily doses from a naturalistic setting were consistent with recommendations based on clinical trials. Olanzapine-treated patients were less likely to experience EPS, any adverse event, or use of anticholinergic medications than risperidone and haloperidol patients were. Olanzapine-treated patients were less likely to receive other antipsychotic medications and more likely to experience a response than risperidone patients.