Thirteen members of a large family presented with a hereditary motor and sensory neuropathy (HMSN); 8 of them also showed more or less prominent signs of myotonic dystrophy (MyD). There were no cases with MyD alone. The disorder showed segregation with genetic markers for the MyD gene on chromosome 19. This was also true for the 5 subjects in which clinically only HMSN had been detected, 3 of whom were young children. This is the first time that a form of HMSN has been found to be coded for by a gene localized on chromosome 19. The syndrome could be caused by an allelic form of the 'common' MyD gene or by two closely linked genes on chromosome 19.