We report observations on the treatment of 66 patients with presumed dopa-responsive dystonia (DRD). Forty-seven of these patients had hereditary disease; 19 had disease of sporadic occurrence. Initial diagnostic confusion with "cerebral palsy" or "spastic diplegia" existed in 16 patients. Several patients benefited from anticholinergic medications and a few from carbamazepine. Levodopa was the most effective treatment in all cases. In the majority, there was an excellent response, with continued long-term clinical stability on levodopa therapy for as long as 10 to 22 years. Four men with sporadic disease and 1 woman with a sister affected with adolescent-onset parkinsonism had similar initial treatment response, but developed "wearing-off" and a less satisfactory response to levodopa within the first few years of treatment. This indicates that some patients with clinical syndromes suggestive of DRD may not have an excellent prognosis on long-term levodopa treatment and may represent misclassified cases of childhood-onset parkinsonism.