Depression is an important and common nonmotor feature of Parkinson's disease (PD) that is associated with significant disability and a negative impact on quality of life. The physician should remain vigilant for symptoms of depression as they may be mistaken for the progression of Parkinson's disease itself. Transient dysphoria that occurs during 'off' periods in fluctuating PD patients must be distinguished from true depression. Antidepressant therapy should be instituted if depression is interfering with the patient's daily function. The use of serotonin reuptake inhibitors and tricyclic antidepressants in the treatment of depression in PD is widespread in clinical practice. Dopamine agonists may be effective in the treatment of milder depression as well. Individual or family counseling may be helpful. In patients with severe depression who are refractory to antidepressant medications, a series of electroconvulsive treatments can be lifesaving. Nonconventional therapies such as transcranial magnetic stimulation are being investigated. © 2004 Elsevier Ltd. All rights reserved.