Dermatomyositis (DM) is an autoimmune disease manifested by muscle weakness and characteristic cutaneous eruptions. Cytomegalovirus (CMV) belongs to the β-herpesvirinae subfamily of herpesviridae that cause morbidity and mortality in immunocompromised patients. With respect to the relationship between CMV and DM, it remains unknown whether CMV plays a pathogenetic role or whether CMV disease is an opportunistic infection due to immunosuppressive treatment. We report two patients with DM who developed cutaneous CMV ulcers within one month after the initiation of systemic corticosteroid treatment. In this context, we retrospectively studied the clinical characteristics of six DM patients with CMV reactivation and the effect of corticosteroid treatment on CMV reactivation in these patients. We also examined possible predictive parameters of CMV reactivation during the course of DM. Our results suggest that CMV reactivation occurs more frequently in DM patients than previously recognized; CMV reactivation occurs regardless of the dosage and duration of corticosteroid administration or the presence of underlying disease. Furthermore, our study shows that a reduction in platelets, serum globulin and IgG levels during the course of DM may be useful predictive parameters for CMV reactivation in patients with DM.