An X-linked adult-onset neurogenic muscular atrophy, chiefly proximal, with late involvement of the distal musculature and medulla oblongata was present in 4 members of a single kindred. Associated in all patients were gynecomastia, impotence and essential tremor. Frederickson type IV hyperlipemia was present in 1 patient. Hormonal stimulation tests in 2 patients elicited a borderline low testicular response in the younger of the 2 and a pathological response in the older patient. On the evidence of these and previously reported cases, Kennedy disease would appear to be characterized by an X-linked proximal neurogenic amyotrophy of adult onset and by a testicular endocrine deficit.