Although several studies have investigated the occurrence of medical and neurological conditions in persons with autism, relatively few reports have focused on the phenomenology and treatment of psychiatric disorders in this population. There is emerging evidence that depression is probably the most common psychiatric disorder that occurs in autistic persons. In this review, we examine the factors that influence the presence of depression in this population, such as the level of intelligence, age, gender, associated medical conditions, and the role of genetic factors and life events. We discuss the various forms of treatment available and highlight the need for early detection.