The clinical course and muscle biopsy findings of four adults with sarcoidosis who developed a myopathy are described. Three patients had evidence of an inflammatory myopathy and elevated CPK. Two patients had no detectable granulomas at muscle biopsy and may represent a separate autoimmune disorder (polymyositis) concurrent with sarcoidosis. Asymptomatic muscle disease in sarcoidosis probably occurs with a much greater frequency than symptomatic disease. Isolated sarcoid myopathy without prior or concurrent organ involvement has been described, but comprehensive autopsy studies to confirm this are lacking. The origin of symptoms associated with granulomas is obscure and may be mediated through the effects of lymphokines and monokines. Corticosteroids seem to play a useful role in therapy, but treatment over a prolonged period may be necessary. The use of cytotoxic agents is largely untested.