This study was conducted to evaluate the inhibin B with FSH and LH levels on spermatogenesis in varicocele patients. The study group consisted of 10 adolescent with left idiopathic varicocele of grade II and III. Blood specimens were obtained from dilated spermatic vein and peripheral vein simultaneously. Peripheral samples were also collected from 7 healthy children as controls. Inhibin B was measured with ELISA inhibin B kits. FSH and LH were analyzed by radioimmunoassay techniques. The results were analyzed using Mann-Whitney U and Spearman's rank tests. A value of p < 0.05 was considered significant. Peripheral FSH, LH and inhibin B levels were the same in the study and control group (p > 0.05). Mean inbibin B levels of spermatic vein were significantly higher than the control and peripheral blood of the study groups (p > 0.05). Preoperative serum inhibin B concentration could not reliably predict a response to varicocelectomy, but the increase in inhibin B levels after treatment might suggest an improvement in testicular function.