Depressive illnesses are common in the general population and are significantly more common in those with physical illnesses. The symptoms of depression may go unrecognised in medical patients, with consequent under-diagnosis and under-treatment. Co-morbid depression is associated with increased morbidity, poorer function, increased healthcare costs and increased mortality. Depressive illnesses are amenable to treatment by both pharmacological and psychological means. Successful treatment can result in improved quality of life as well as improved function, mortality and overall outcome in the physical disorder. It is therefore important that medical doctors are aware of the symptoms, diagnosis and management of depressive illness.