Of 86 patients who had undergone unilateral testicular torsion the fertility in 36 patients could be examined 1-9 years later. The testis in 27 patients (= 75%) was surgically untwisted. Of 9 patients (= 25%) the testis was removed because of marked hemorrhagic infarction. Fixation of the contralateral testis was prophylactically performed in all cases. The testis of all patients who had undergone the detorsion within the first 22 h were saved and there was no significant difference of the testicular volume compared with the contralateral side. An atrophy of the contralateral testis following prophylactical fixation was never observed. In most of the 36 patients the fertility was diminished: Seminal analysis revealed an oligozoospermia in 44%, a teratozoospermia in 20%, an asthenozoospermia in 20% and a normozoospermia in 16% only. This result was independent of the duration of the torsion. There was no difference in the group of patients with detorsion and the group with orchidectomy. The endocrinological examination revealed a statistically significant correlation between FSH and sperm density and between FSH and the duration of the torsion. But both correlation coefficients were less than 0.5 and are therefore without any clinical relevance. Testosterone, LH and prolactin were normal in all cases.