Delayed-onset dystonia due to perinatal or early childhood asphyxia. We report 10 patients with delayed-onset dystonia associated with perinatal asphyxia and 2 associated with asphyxia in childhood. In the perinatal group, the mean age of onset was 12.9 years. Among these patients, dystonia continued to progress for a mean of 7 years, and as long as 28 years. These patients had moderate motor disability; none was wheelchair-bound, and thus their prognosis was better than that of the childhood-onset idiopathic torsion dystonias. The most frequently beneficial drugs were anticholinergics. Since some of these patients closely resembled cases of idiopathic torsion dystonia, the prior occurrence of asphyxia should be used as a criterion of exclusion for that diagnosis. 