The natural history of cervical dystonia (spasmodic torticollis) was investigated in a population-based study in Rochester, Minnesota. Eleven new cases were identified with onset during the 20-year period 1960-1979. The overall incidence rate was 1.2 per 100,000 person-years (95% confidence interval 0.5-1.9) with a female:male ratio of age-adjusted incidence rates of 3.6:1. A unitary etiology was not apparent: injury antedated onset in four of the 11 patients, whereas six had documented thyroid disease and four had diabetes. A family history of movement disorder was recorded for only one subject. Only one of the cases would have been classified as moderate in severity; the others were mild. In follow-up through 1993, progressive disability was noted in only two patients, and two others went into remission. Three cases of intracranial aneurysm were confirmed, two of which produced fatal subarachnoid hemorrahage. A third death was due to amyotrophic lateral sclerosis.