Between 1970 and 1973, 135 patients with Parkinson's disease were seen and examined prior to the initiation of levodopa. The age of onset was 59.1 years and average duration of disease before beginning levodopa was 5.6 years. In 12 patients (9 per cent) the disease had had its onset when the patients were in their 20's and 30's. Only four patients were judged to have postencephalitic parkinsonism. The remaining 131 patients were considered to have idiopathic parkinsonism. A moderate dementia was present in 29 patients (22 per cent). The dementia was considered a separate degenerative process and not directly related to the parkinsonism. A classification system was devised which characterized patients by the presence or absence of four major signs: rigidity, tremor, bradykinesia and gait disturbance. These signs were graded as to degree of severity. The significance of these major signs was discussed as was the significance of several of the minor signs: speech impairment, dysphagia, sialorrhea, seborrhea, and orthostatic hypotension. The occasional association of parkinsonism with amyotrophy, pyramidal tract signs, and cerebellar dysfunction was also discussed. The differential diagnosis of Parkinson's disease from essential tremor, normal pressure hydrocephalus, striatonigral degeneration, pseudobulbar palsy, the rigid form of Huntington's disease, and progressive supranuclear palsy was discussed. Some remarks on the effects of levodopa on the major and minor signs of parkinsonism were made.