A 47-year-old was referred for chronic thrombocytopenia of 80-90 × 109/L and splenomegaly. He had been treated unsuccessfully for immune thrombocytopenia. Previous bone marrow biopsies were nondiagnostic and an earlier liver biopsy showed steatosis. In addition to splenomegaly, he presented with xanthomas. Hemoglobin 12.3 g/dL, haptoglobin 2 mg/dL, indirect bilirubin 2.4 mg/dL, and an elevated absolute reticulocyte count 240 mil/L. Direct antiglobulin test and flow cytometry for PNH were negative. Osmotic fragility was increased. Peripheral smear revealed stomatocytes and macrothrombocytes consistent with hereditary sitosterolemia. The patient's sitosterol level was 166.0 mg/L (0-5) and campesterol 84.9 mg/L (0-7). Sitosterolemia is a rare autosomal recessive disorder involving the ATP-Binding Cassette G (ABCG) proteins ABCG5 and ABCG8 that help prevent sterol absorption and promote excretion of plant sterols. Absent their function, plant sterols accumulate