Multiple myeloma is a cancer of plasma cells that produce monoclonal immunoglobulin, and the neoplastic plasma cells typically accumulate in the bone marrow with occasional involvement of other organs. Pleural effusion that is associated with multiple myeloma has been infrequently reported (<6%) and myelomatous pleural effusion is extremely rare (<1%). A 73-year-old woman was admitted to the department of dermatology for skin lesions on both arms and both ankles. A chest radiograph taken on admission showed a nodular lesion in the right upper lung and pleural effusion. Analysis of the pleural fluid revealed many atypical plasma cells, elevated levels of IgA (27.95g/L) and lambda light chain (9.16g/L), and monoclonal IgA-lambda paraprotein on immunofixation. The serum concentrations of IgA were elevated (33.08g/L) while the concentrations of IgG and IgM were decreased. Bone marrow aspirate smears contained increased levels of immature-appearing atypical plasma cells. This is only the third case of myelomatous pleural effusion that has been reported in Korea.