[Excellent growth following testosterone replacement therapy in identical twin with bilateral anorchia].

Bilateral anorchia is defined as the complete absence of testicular tissue with a normal male karyotype and phenotype. Although the precise etiology is not well understood, mechanical causes during or after testicular descent have been suggested, while genetic factors have also been reported. We treated a patient with bilateral anorchia who obtained excellent growth bytestosterone replacement therapyas compared with his normal identical twin. The patient was diagnosed with negative elevation of testosterone after hCG administration and surgical exploration confirmed the absence of a testicular structure. We began testosterone replacement therapyfrom 13 years old with the goal of matching the development of his brother. Four months after initiating therapy, the patient showed voice breaking and pubic hair growth. Thereafter, there were scant differences in height and secondarysexual characteristics as compared with his brother.