summary   Parkinson's disease is frequently accompanied by depression which can have a negative effect on a patient's cognitive performance, quality of life and activities of daily living. Because Parkinson's disease and depression have a number of symptoms in common, it is sometimes difficult to distinguish the two disorders. Furthermore, the overlapping pathophysiology may make it difficult to treat depressive symptoms without influencing the patients motor or cognitive functions. This narrative review summarises our current knowledge concerning the epidemiology, etiology, pathophysiology and treatment of depression in patients with Parkinson's disease. Clearly, however, many questions remain unanswered. In particular, research is needed into the efficacy of currently available treatments for depression so that it becomes possible to develop evidence-based guidelines.