A familial myopathy affecting a man, his three daughters, and one of his brothers is reported. The quadriceps muscle was predominantly involved, with aching pain as an early feature, and later prominent areas of hypertrophy projecting from patches of atrophy gave the quadriceps a most striking and unusual appearance. Presentation was in adult life, and the course was relatively benign, pelvic girdle and hand muscles becoming involved later. The evidence suggests a hereditary selective muscular dystrophy rather than polymyositis, although a hereditary form of spinal muscular atrophy could not be excluded entirely.