Clinical, electrophysiological, and histopathological studies of some members of a family with dominantly inherited hypertrophic neuropathy are presented. Twenty-five members were studied. Seventeen were abnormal on clinical examination. Their ages varied from 2 1/2 to 78 years. Age at onset in 14 of the 17 varied between 2 1/2 and 56 years. Pes cavus and palpable nerve thickening were present in more than half of the affected individuals. All patients had areflexia. Fifteen of the 17 had distal motor weakness as well as mild to moderate sensory impairment. Motor weakness affecting the proximal hip and shoulder girdle muscles was seen in 13 patients. Four patients gave a history of trigeminal neuralgia. Motor nerve conduction velocities were markedly impaired in all the clinically affected members. These studies were normal in the 8 unaffected members. Motor conduction velocities of the proximal segment of the ulnar nerve were slower compared to the distal segment in almost all the affected members. There was no significant correlation between the degree of clinical disability and the extent of impairment in the motor nerve conduction velocities. Sural nerve biopsies were studied. These observations are discussed.