Objectives: Dermatomyositis and polymyositis (DM/PM) are associated with neoplasms. The aim of the present study is to compare our experience in Israel with other published data. Methods: Thirty-five adult patients with DM/PM, admitted to Sheba Medical Center during the 11-year interval between 1984 and 1994, were studied for the prevalence and features of malignant diseases. Patients with DM/PM alone and with DM/PM and malignancy were identified by using the hospital computer system. The manifestations of DM/PM and features of the malignant diseases were abstracted from the patients' charts. The presence or absence of malignancy and the type of cancer were verified in the National Cancer Registry. Results: There were 15 men and 20 women. The mean age at the onset of the disease was 53 ± 18 years. A total of 15 had PM and 20 DM. Malignancies occurred in four patients with PM (27%) and in nine with DM (45%) a frequency 12.6 times higher than in the general population. In six patients, the malignancy and the DM/PM were diagnosed simultaneously; in four before and in three after the appearance of the DM/PM. Hematologic, gastrointestinal, breast, ovarian, and lung tumors, malignant melanoma, and metastatic carcinoma of unknown primary were found among our patients. Eight DM/PM patients with malignancy died during the study period of infection, pulmonary embolism, and tumor spread. Conclusions: Our study found that DM/PM is associated with high rates of malignancy and mortality.