MYOCLONUS may be a symptom in a wide variety of diseases which affect the central nervous system (CNS). Myoclonic jerking may occur in the course of a benign "idiopathic" convulsive disorder, as the only symptom of a nonprogressive disorder in some families (essential myoclonus), or as part of a constellation of symptoms in certain progressive degenerative diseases. The purpose of this communication is to present the clinical details of a family in which the occurrence of myoclonus, cerebellar ataxia, and deafness in several generations is thought to represent a distinct genetically-determined disorder. The nosology and relationships between this family and the cases previously described by Unverricht,1 Lundborg,2 Lafora,3 and Hunt4 will be discussed. Report of Cases CASE 1.—The proband (V-4, Fig 1) is a 32year-old white man who was admitted to the University of Kansas Medical Center in April 1967 for evaluation of progressive hearing loss