XYY syndrome: a 13-year-old boy with tall stature.

When evaluating the underlying causes of tall stature, it is important to differentiate pathologic tall stature from familial tall stature. Various pathologic conditions leading to adult tall stature include excess growth hormone secretion, Marfan syndrome, androgen or estrogen deficiency, testicular feminization, and sex chromosome anomaly, such as Klinefelter syndrome and XYY syndrome. Men with 47,XYY syndrome can exhibit multiple phenotypes. A 13-year-old boy visited the hospital for evaluation of tall stature. The boy had no other physical abnormalities except tall stature. All biochemical and imaging studies were within the normal ranges. He was diagnosed with XYY syndrome in this chromosome study. When evaluating men with tall stature, XYY syndrome should be ruled out.