(Communicated by Saj iro MAKINO, M. J. A., May 12, 1982) It has been known that Klinefelter's syndrome is associated occasionally with myeloprolif erative disorders, particularly in a majority of cases with different forms of leukemia. The literature refers to only one case of polycythemia vera in association with this syndrome (Geraedts et al., 1980) . In this paper are reported the chromosomes of a male patient who had symptoms and signs of Klinef elter's syndrome with diabetes mellitus and developed later polycythemia vera.Case report. The patient was born in 1913 between a 48-yearold father and a 29-year-old mother. He married at the age of 26 years, but has no children. He is the third of five siblings, and all the siblings have children except the youngest brother who died in the World War II. There is no consanguinity in his family. Diabetes mellitus was diagnosed at the age of 50 years. At the age of 62 years, conj unctival congestion and erythema of the hands were noted. His red blood cell count was found to be markedly elevated at the age of 65 years. Then he was referred to our clinic due to polycythemia and diabetes mellitus.On physical examinations the patient was 171 cm tall, weighed 65 kg, and had an arm span of 175.5 cm (Fig. 1). His skin was deep red in color on the cheeks, lips, ears, tip of the nose and distal portions of the extremities. Bulbar and palpebral conjunctivae were markedly congested. He had bilateral gynecomastia and cubitus valgus, and a simian crease on the right hand. The axillary and pubic hair was scanty, and the testes were small measuring 2.5 by 1.5 cm on both sides. Hepatosplenomegaly was noted.Hematological examinations revealed RBC 938 x 104/cmm, Hb 24.0 g/dl, Ht 79.2% and WBC 12,400/cmm with 78% neutrophils and 8 % eosinophils. Platelet count was 7.2 x 104/cmm, while it was 45.3 x 104/cmm after a series of phlebotomy totaling 740 ml. Erythrocyte sedimentation rate was 0 mm in one hour. Blood chemistry