A 60-year-old woman was admitted to our hospital with anemia and thrombocytopenia. Serum testing showed platelet-associated IgG elevation and she was positive on the direct and indirect Coombs tests. Together with bone marrow examination, these findings indicated a diagnosis of Evans syndrome. At diagnosis, she also had an IgM-κ type of monoclonal gammopathy of unknown significance. Initially, we administered steroids and her hemolytic anemia showed improvement. In contrast, only transient recovery of platelet counts was observed and her platelet counts rapidly decreased after steroid dose reduction. Thus, we treated her with a TPO-agonist, romiplostim. During the clinical course, she showed gradual serum IgM elevation. We thus performed another bone marrow biopsy and diagnosed her as having Waldenström's macroglobulinemia (WM). We started treatment with rituximab for WM. Together with the serum IgM reduction, she showed marked improvement of thrombocytopenia. This is a very rare case of WM initially presenting as autoimmune hemolytic anemia and immunethrombocytopenia associated with IgG class auto-antibody. Our experience suggests the usefulness of rituximab and romiplostim for the treatment of immunethrombocytopenia associated with WM.