Long periods of antipsychotic pharmacotherapy are often necessary because many of the psychotic conditions indicated for antipsychotics are chronic in nature. Atypical antipsychotic agents, with a broader response profile and fewer side effects, may increase the likelihood of achieving longer periods of pharmacotherapy relative to typical antipsychotic agents. OBJECTIVE: This study compares the duration of continuous therapy between atypical and typical antipsychotics in the naturalistic care setting. METHOD: Three years of medical claims data from a large U.S. prescription database were analyzed for 56,682 patients with at least one antipsychotic prescription between 5/1 and 7/31/1995. A patient's first antipsychotic prescription (the index prescription) during this interval was used to classify each patient into an atypical or a typical antipsychotic cohort. Patients were further classified into "new" or "continuing" cohorts based on whether or not the patients had received any antipsychotic prescriptions during the 12 month period preceding their index prescriptions. Duration of continuous therapy, defined as the total number of antipsychotic days supplied to a patient prior to a period of 31 or more days with no antipsychotic medications, was tracked over a two year period after the index prescription. RESULTS: Duration of continuous therapy was 201±266 (mean±SD) days for all patients. For atypical antipsychotics, the duration of continuous therapy was 301±299 days for new users and 347±308 days for continuing users. In contrast, the duration of continuous therapy for typical antipsychotics was 136±229 days for new users and 257±278 days for continuing users. CONCLUSION: Patients on atypical antipsychotics have a longer duration of continuous therapy.