A case of autoimmune disease-associated lymphadenopathy (ADAL) in the lymph nodes linked to well documented dermatomyositis is presented. A 49-year-old Japanese woman was affected by a left axillary and a left inguinal lymphadenopathy at the onset of disease. A biopsy specimen taken from a left inguinal lymph node showed distortion of the nodal architecture and polymorphous lymphoid infiltration containing many plasma cells and plasmacytoid cells with scattered transformed lymphocytes, as well as a large number of capillaries. The polytypic nature of B-lymphocytes was demonstrated by immunohistochemistry and polymerase chain reaction. Epstein-Barr virus-associated lymphoplasmacytic infiltrates may occur in patients immunosuppressed by methotrexate administered for the treatment of dermatomyositis. However, Epstein-Barr virus-encoded small RNA-positive cells were not identified by in situ hybridization. Moreover, the patient had no history of methotrexate therapy.