BACKGROUND: In controlled studies of patients with schizophrenia, the atypical antipsychotic quetiapine, 300 mg/day, has been shown to be as effective in the treatment of positive and negative symptoms as haloperidol. However, little is known about the efficacy of quetiapine in patients with psychotic mood disorders. The purpose of this study was to assess the efficacy of quetiapine in the treatment of psychotic mood disorders in comparison with nonaffective psychotic disorders and identify clinical factors associated with quetiapine response. METHOD: In a naturalistic setting, by reviewing medical records, we assessed response to quetiapine and factors associated with response to quetiapine in 145 consecutive patients newly treated with the drug at a nonprofit academic psychiatric hospital. These patients had received a discharge diagnosis of bipolar disorder (manic, mixed, or depressive type), major depression with psychotic features, schizophrenia, schizoaffective disorder (bipolar or depressive type), delusional disorder, or psychosis not otherwise specified (NOS) according to DSM-IV criteria. RESULTS: Patients with a diagnosis of bipolar disorder, manic, mixed, or depressed and schizoaffective disorder, bipolar type displayed higher response rates (> 74%) compared with patients with schizophrenia. However, this finding did not achieve statistical significance. A diagnosis of major depression with psychotic features (p = .02) and longer duration of illness (p = .03) were associated with less chance of responding. CONCLUSION: Quetiapine may be a useful alternative or adjunctive treatment for patients with bipolar and schizoaffective disorders.