Depression associated with Parkinson's disease (PD) is common and affects 25 to 40% of patients. Recognition of the signs and symptoms of depression associated with PD is essential for clinical practitioners. Treatment of depression in this subset of patients can have a direct and dramatic impact on functional disability and quality of life. A review of the literature concerning depression and depression associated with PD was undertaken, with specific attention given to disease mechanisms, clinical presentation, association with thyroid disease, and the principles of management and treatment. Specific signs and symptoms of depression can be easily identified in patients with PD. Practitioners should be aware of these signs and symptoms when diagnosing and treating depression associated with PD. Practitioners should also be aware of the pros and cons of each treatment option and should choose a therapy appropriate for each individual patient's needs. It is important to identify the features of depression associated with PD in order to render early diagnosis and institute practical and efficacious therapy.