Our aim was to investigate the semen variables and hormone profiles among transplant patients who received kidneys during adolescence. Seven postpubertal transplant patients who underwent successful renal transplantation during adolescence (13-19 years; 3 were preemptive) were enrolled in our clinical follow-up. Serum levels of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone were checked together with the semen analysis. The ages of the patients ranged from IS to 25 years (median, 22 years). The median age was 15 years (range, 12-18 years) at initial presentation. The median time between initial diagnosis and transplantation was 12 months (range, 2-60 months). The median follow-up after transplantation was 51 months (range, 23-134 months). Three of the seven patients had unilateral low testicular volume. The renal function tests were within normal limits, as well as serum levels of prolactin, FSH, LH, and testosterone. Sperm counts ranged from 0.2 to 55 million/mL (median, 1.7 million/mL). Only I patient (14.2%) had normal sperm parameters. Oligoteratozoospermia (low sperm count and defects in morphology) was observed in 1/7 (14.2%). asthenoteratozoospermia (low levels of motility and defects in morphology) in 1/7 (14.2%), and all parameters were abnormal in 4/7 (57.1%) cases. Our data suggest that in contrast to adult patients, semen variables are severely affected and spermatogenesis does not improve after renal transplantation when the patient was subjected to uremia before or during adolescence, the crucial period for spermatogenesis.