48, XXYY is a very rare sex chromosome aneuploidy, characterized by both an extra X and Y chromosome with a prevalence of 1:18,000–1:40,000. Most patients are diagnosed prenatally by cytogenetic examination of amniotic fluid, or during the first years of life because of severe developmental delay, cognitive impairment and behavioural disorders. This syndrome shares two findings with Klinefelter syndrome, namely tall stature and hypergonadotropic hypogonadism but at this time no genital anomalies have been reported in patients with this tetrasomy. We describe a 48, XXYY neonate and a clinical picture characterized by small penis, bifid scrotum, scrotal hypospadias and testes palpable in the labioscrotal folds.
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