Objective To investigate the clinical characteristics and risk factors for thromboembolic events in patients with idiopathic inflammatory myopathy (IIM). Methods We retrospectively analyzed 1144 consecutive patients with IIM for arterial and venous thromboses and compared them with age- and sex-matched IIM patients without thrombosis. Logistic regression analysis was used to analyze risk factors for thrombosis. Results Twenty-four (2.1%) patients had arterial or venous thromboses (mean age, 62.6 +/- 11.6 years; range, 33-81 years). Thromboembolic events occurred in 54.2% (13/24) of patients within 6 months before or after IIM diagnosis. Thrombosis patients had a higher Cutaneous Dermatomyositis Disease Area and Severity Index score (p = 0.028), higher myositis disease activity assessment visual analogue scale score (MYOACT) (p < 0.001), and a greater proportion of them had varicose veins (p = 0.001), surgical history in the past 3 months (p = 0.039), malignancy (p = 0.018), and infection (p < 0.001). The manual muscle test 8 score (p < 0.001) and albumin level (p = 0.003) were lower in thrombosis patients. There was no significant difference between the two groups in glucocorticoid pulse therapy; however, intravenous immunoglobulin therapy was more commonly used in thrombosis patients (p = 0.04). In multivariable regression models, malignancy, infection, longer duration of glucocorticoid treatment, and higher MYOACT were risk factors for thrombosis. The cumulative survival time of IIM patients with thrombosis was significantly shorter than that of controls. Conclusions Malignancy, infection, longer duration of glucocorticoid use, and increased myositis disease activity are risk factors for thrombosis. Patients with these risk factors should undergo screening for thrombosis.