[A case of 48 XXYY Klinefelter's syndrome]

We observed a patient with 48 XXYY Klinefelter syndrome who visited our hospital because of a short penis as chief complaint. The patient was a 21-year-old, tall and obese man. He had gynecomastia. The penis was short and bilateral testes were underdeveloped. Endocrinologically the LH and FSH showed high level and the testosterone was low. A diagnosis of very rare 48 XXYY Klinefelter was made based of the chromosomal analysis.