Sertraline and other SSRIs have a relatively favorable side-effect profile and are widely prescribed. We report the emergence of psychotic symptoms during treatment with sertraline in four patients. Three of these patients had a history of psychotic illness and were on antipsychotic medication, when sertraline was added. The psychotic symptoms emerged within 3 days-7 weeks of starting sertraline and resolved on its discontinuation. We wish to alert clinicians to the possibility that sertraline may provoke or exacerbate positive psychotic symptoms, particularly in patients on neuroleptics, with a previous history of psychosis.