A 62-year-old man had chronic myelomonocytic leukemia (untreated) for a period of 8 years. He developed a sudden, spontaneous rupture of the spleen and a splenectomy was performed. Grossly and microscopically the spleen showed peliosis. The blood-filled cavities were similar to the pseudosinuses described in the spleen of hairy-cell leukemia. The lesion common to these disorders apparently is a progressive disappearance of lining cells and of ring fibers.