A family study in 29 patients with idiopathic adult-onset blepharospasm (n = 16) and cranial-cervical dystonia (n = 13) was undertaken by examining 189 first-degree relatives. Six relatives with dystonia were identified in 6 families. A further 3 affected relatives, now deceased, were from 2 other families. All the secondary cases were parents or siblings. There was a tendency for affected relatives to have the same type of dystonia of index patients. To assess the significance of secondary cases we compare the incidence of affected siblings between probands and their spouses. Dystonia was found in 5 out of 120 proband siblings whereas none of the 142 spouse siblings was affected (p < 0.05). Segregation analysis suggested an autosomal-dominant transmission and reduced penetrance or, alternatively, polygenic inheritance.