The association of malignancy with dermatomyositis and polymyositis has been questioned. During the last 20 years (1956 to 1975), we have studied 58 cases of myositis that met predefined diagnostic criteria. These cases were analyzed for the frequency of malignancy, prognosis, and the value of a diagnostic test series for malignancy. A significantly greater frequency of malignancy was found with dermatomyositis than with polymyositis. The prognosis of dermatomyositis and polymyositis appears to be altered in the presence of malignancy. In the absence of malignancy, the prognosis is similar in the two forms of myositis. Lastly, the value of a screening laboratory and roentgenographic investigation for the presence of occult malignancy beyond a thorough history, physical examination, and the use of basic laboratory tests such as complete blood count, stool gualac test, urinalysis, multiphasic analysis, and chest roentgenogram was not documented by this study.