To investigate the duration of a prodromal phase before the onset of the classic symptoms of idiopathic Parkinson's disease, the authors conducted a retrospective case-control study of 60 patients with Parkinson's disease and 58 age- and sex-matched control subjects, covering the decade preceding the onset of classic Parkinson's disease. The symptoms were derived from files of the patients' general practitioners. Compared with control subjects, patients pre-Parkinson's disease had more central nervous system, psychologic, musculoskeletal, and cardiovascular (i.e., autonomic) symptoms. Patients pre-Parkinson's disease also made more visits to general practitioners and medical specialists. The results indicate that the onset of classic parkinsonism is frequently preceded by a prodromal phase lasting from 4-6 years.