Patients/Method: Twenty-seven adults who underwent an orchidopexy before 2 years of age have recently had their spermiograms analyzed. Results: Sixty-three percent of them had a normal sperm count; their germ cells had undergone the second stage of maturation and adult dark (Ad) spermatogonia were present at the time of surgery 20–25 years earlier. In contrast, 37% of them were infertile despite a seemingly successful orchidopexy; they had impaired second-step germ cell maturation and Ad spermatogonia were absent at orchidopexy. Conclusions: Transformation of gonocytes into Ad spermatogonia is crucial for fertility. This underscores the importance of a testicular biopsy at orchidopexy in order to identify those who could benefit from early LH-RH treatment after orchidopexy.