Normal sexual function is a biopsychosocial process; sexual dysfunction almost always has organic and psychological components and requires multidisciplinary, goal-directed evaluation and treatment. Factors such as aging, declining testosterone levels, medical illness, certain medications. and comorbid depressive illness can contribute to sexual dysfunction. Erectile dysfunction is one of the more common male sexual dysfunctions encountered in the clinical setting. Comorbidity between erectile dysfunction and depressive illness is high, but the causal relationship is unclear. The psychosocial distress that often accompanies erectile dysfunction might stimulate the development of depressive illness, or, as some data suggest, depression might cause erectile dysfunction. This article reviews the literature on the relationship between depression and erectile dysfunction, as well as the design of a new study that may provide some answers, and concludes that erectile dysfunction is a common, treatable condition that may cause or be the result of depression. Recent data suggest that sildenafil is an effective treatment for erectile dysfunction in men with comorbid depression. Erectile dysfunction should be considered a multifactorial condition that may require a multidisciplinary approach to treatment, especially when depression is present.