A 29 year old man presented to primary care with anxiety and depression that had worsened since childhood. Further questioning revealed a history of poor school performance, poor body image, and poor self esteem. On physical examination, the patient’s height was 189 cm and he had narrow shoulders, wide hips, sparse facial hair (which he shaved once every two months), and small, firm testicles. He was found to have elevated luteinising hormone and follicular stimulating hormone concentrations, low serum concentrations of testosterone, absent sperm on semen analysis, and a karyotype of 47,XXY. Klinefelter’s syndrome is the clinical result of an additional X chromosome in males (47,XXY), although other chromosome abnormalities (such as 46,XY/47,XXY mosaicism; 48,XXXY; 49,XXXXY) account for 10-20% of cases.1 2 Classic clinical findings include infertility, small testes, hypergonadotropic hypogonadism (elevated luteinising hormone and follicular stimulating hormone concentrations with low or low to normal testosterone concentrations), decreased facial and body hair, gynecomastia, tall stature with eunuchoid features, and psychosocial morbidity.1 3 #### How common is Klinefelter’s syndrome?