Eleven patients met rigid criteria for having both polymyositis and systemic lupus erythematosus (SLE). The patients differed little in clinical features when compared with patients who had SLE and polymyositis in a previously reported series. The overall mortality rate of 18% and the finding that 56% of survivors were asymptomatic at latest follow-up (average four years) suggest that the prognosis for this subgroup of patients may be more favorable than that for patients with rheumatoid arthritis and scleroderma complicated by polymyositis and may be comparable to the prognosis of the overall group of patients with polymyositis.