Descriptions of individuals with Williams syndrome (WS) and co-morbid major depressive disorder (MDD) with psychotic features have not appeared in the literature. In addition to reviewing previous reports of psychotic symptoms in persons with WS, this paper introduces clinical histories and therapeutic management strategies for three previously unreported adults with WS diagnosed with co-morbid MDD with psychotic features. Co-morbid medical disorders common in WS are highlighted with regard to safe and appropriate pharmacological treatment. The importance of assessment for co-morbid MDD with psychotic features in individuals with WS is emphasized.