OBJECTIVE: To identify potential risk factors and the yield of routine screens for early detection of malignancy associated with dermatomyositis (DM) and polymyositis (PM). DESIGN: Retrospective study of malignancies in all patients with DM or PM followed up between the years 1981 and 2000 and a review of the relationship of DM and PM to malignancy, the usefulness of various tests or examinations for malignancy search, and the patients' course. SETTING: Departments of internal medicine and dermatology in a teaching hospital. PATIENTS: Forty consecutive adult patients with DM (33 cases) or PM (7 cases). MAIN OUTCOME MEASURES: (1) Rate of false-negative results of routine workup and yield (percentage of positive results) of blind malignancy search and (2) comparison of 16 characteristics in patients with malignancy vs those without. RESULTS: Malignancy occurred in 16 patients: 13 with DM and 3 with PM. In all cases, the diagnosis of malignancy was made concurrently with or shortly after the diagnosis of DM or PM. Factors associated with malignancy were recruitment in the internal medicine department (P =.02), constitutional symptoms (P<.01), a rapid onset of DM or PM (P =.02), the lack of Raynaud phenomenon (P<.01), and a higher mean erythrocyte sedimentation rate (P<.01) and creatine kinase level (P<.01). Initial routine search failed to discover 4 malignancies, 3 of which were discovered at an advanced stage by more extensive investigations. The positive result yield of blind malignancy search was only 13% (11 of 87), but reached 28% (5 of 18) for blind abdominal-pelvic and thoracic computed tomographic scans. CONCLUSION: Extensive search for malignancy, particularly computed tomographic scans, may be warranted in at least a subset of patients with DM or PM and risk factors of malignancy.