The occurence of extranuchal dystonia, facial spasm, parkinsonian symptoms (facial masking, bradykinesia, rigidity), tremor and family history of tremor was tabulated in a group of 30 patients with IST. The incidence of extranuchal dystonia increased as severity of IST increased. There was a strong trend for severity of extranuchal dystonia to increase as severity of torticollis increased, which was significant (p less than 0.001). There was a similar trend for severity of facial spasm to increase with increasing severity of torticollis (p less than 0.025). Parkinsonian features were seen in 10 of 30 patients, and in three the diagnosis of Parkinson's disease could be entertained. Tremor was seen in 26 of 30 patients being mild in 12, moderate in 11, and severe in three. A family history of tremor was present in 16 of 28 cases for whom history was available (12 primary, four secondary relations). The results are most consistent with the hypothesis that IST is a variant of DMD with tremor as an integral part of the disease and tremor represents a forme of the disease in family members.