Malignant lymphoma has been infrequently reported in the course of systemic lupus erythematosus (SLE). We report a case of primary malignant lymphoma of the spleen, an unusual site of primary lymphoma, complicating the course of systemic lupus erythematosus (SLE). Our patient had been treated with low dose prednisone and hydroxychloroquine only, and her lupus was quiescent at the time of presentation with the lymphoma. Thus primary malignant lymphoma should be considered in the differential diagnosis of splenomegaly in SLE.