Depressive symptoms and syndromes are common in the medically ill, although they are frequently unrecognized and untreated. The authors review the epidemiology, differential diagnosis, clinical presentations, and response to treatment of this clinical problem. They address such methodological issues in the current literature in this area as the advantages and limitations of standardized assessment measures and discuss treatment modalities for depression in the medically ill, including antidepressant medication and ECT. This clinical problem warrants attention for a variety of reasons: its prevalence, associated morbidity, and treatability. Elucidation of the mechanisms of depression in the medically ill may also contribute to a broader understanding of depression in other populations.