Clinical depression is a relatively common, and yet frequently overlooked, source of suffering among patients with cancer. All patients who face a life-threatening diagnosis such as cancer experience a normal albeit painful emotional reaction, but a substantial minority will become clinically depressed. This article reviews some basic information that oncology practitioners may find helpful in identifying patients at risk of experiencing a major depression. A brief overview of the epidemiology, diagnostic criteria, screening approaches, and special issues, such as depression in the elderly, high-risk populations, and suicide is also provided.