Peripheral neuropathy was investigated in thirty-one patients with myotonic dystrophy (MyD) and sixteen relatives. Using standard electrophysiological criteria, a sensorimotor axonal peripheral neuropathy was found in 14 MyD cases (45%) and not in unaffected first-degree relatives. The whole group of the MyD patients showed significant impairment of mean motor and sensory conduction values, compared with controls. The presence of polyneuropathy was correlated with the patients' age and the severity and duration of the clinical manifestations of MyD.