This paper reviews the diagnosis and medical treatment of the major affective disorders. Patients with severe mood disturbances are frequently seen by the family physician. The diagnosis may be delayed since the patient may focus predominantly on somatic concerns which may mimic physical illness. The characteristics, course, and differential diagnosis of depression and mania are discussed. Antidepressants and lithium therapy greatly improve the prognosis of these disorders; monoamine oxidase inhibitors and neuroleptics are indicated for special subtypes of depression. Dosage schedules, interactional effects, adverse and toxic effects are reviewed for tricyclic antidepressants and lithium.