Patients with neurologic illness frequently develop secondary mood disorders that are broadly categorized as unipolar or bipolar. Accurate diagnosis is essential because the treatment of unipolar disorders is markedly different from that of bipolar disorders. Aggressive treatment of mood disorders improves quality of life, reduces morbidity and mortality, and may prevent worsening of both psychiatric and neurologic disease. Antidepressants and psychotherapy are both effective for patients suffering from depressive disorders. Choice of antidepressant depends on the patient's particular symptom complex; medication side effects, which may exacerbate the underlying neurologic condition; potential interactions with other drugs; and costs. Bipolar disorder associated with neurologic illness typically requires treatment with mood stabilizers such as lithium, divalproex sodium, carbamazepine, or verapamil. Although psychotherapy in combination with pharmacologic therapy improves the outcome in bipolar illness, psychotherapy alone is not effective for this condition. Electroconvulsive therapy is an effective treatment for both depression and mania. It may have particular usefulness in Parkinson's disease, for which it has been shown to improve the movement disorder itself. Treatment of bipolar disorder, psychotic depression, or refractory depression is complicated and should be referred to a psychiatrist.