Testosterone treatment of an XXYY male presenting with aggression: a case report.

A hypogonadal male with 48 XXYY Karyotype--a rare Klinefelter's syndrome variant--is presented with review of the literature. Cautious initiation of testosterone replacement therapy to our patient was associated with sexual maturation and, interestingly enough, disappearance of his longstanding aggressive fantasies and behaviors towards females. An explanatory hypothesis is proposed and clues for early detection of the syndrome are suggested.