Of 105 cases seen over 12 years with mean 4 years followup, there were 69 with polymyositis (PM) and 36 with dermatomyositis (DM). and in 43 this complicated another connective tissue disease (CTD). Primary PM had onset a decade later than others and most severe myopathy occurred in DM. Earliest symptoms were polyarthritis and Raynaud's phenomenon with frequent sicca syndrome (51%). The less than universal prevalence of elevated muscle enzymes (68%), myopathic electromyography (86%). and abnormal muscle biopsy (78%) emphasizes the need for complete evaluation in all cases. Improvement occurred in 69% overall, including all 23 given no therapy or low dose corticosteroids and 59% of the remainder who received high dose corticosteroids with added cytotoxics in one-quarter. Outcome was worse in older patients and in those where weakness exceeded 4 months before diagnosis. Eight of 19 deaths were due to myositis or its therapy which also caused considerable morbidity. Malignancy in 16 cases was temporally related to myositis in half of these cases.