Splenic marginal zone lymphoma (SMZL) is a rare low-grade B-cell lymphoma accounting for less than 1% of lymphoid neoplasms and is often associated with autoimmune disorders. A 48-year-old woman presented with severe anemia due to steroid-refractory cold agglutinin disease (CAD), and was referred to our hospital for management of progressive systemic illness and high fever. On admission, she showed elevated serum soluble IL-2R and mild splenomegaly. PET/CT revealed FDG accumulation in the spleen and bone. She was pathologically diagnosed as having splenic marginal zone lymphoma by splenectomy and received 8 cycles of rituximab every 2 weeks, resulting in marked improvement of anemia. Lymphoma cells were positive for CD20/CD11c/CD13, phenotypically compatible with SMZL. We report herein the characteristic features of SMZL, and appropriate procedures for diagnosis and treatment.