The aim of our study was to determine hormonal or biochemical markers in patients with clinically palpable left varicocele but without a history of infertility, with especial emphasis on nitric oxide, related with improved seminal parameters after varicocelectomy. Semen samples were obtained from 202 patients with left varicocele grade II or III. Nitric oxide levels in seminal plasma were determined by the Griess technique. Testicular volume was determined ultrasonographically in both testes and hormonal profile was measured. The post-operative sperm concentration increased significantly in patients with normal sperm count or moderate oligozoospermia, but we did not find an increment in sperm count in patients with mild and severe oligozoospermia after surgery. The mean percentage of normal motility significantly increased after surgery, but we did not observe a significant increment in morphologically normal sperm count and testicular volume after varicocele repair. Moreover, we did not find any correlation between nitric oxide concentrations and severity of oligozoospermia, asthenozoospermia or abnormal sperm morphology in this population. It is concluded that in the general male population, varicocele repair is not associated with an improved semen profile in all cases. We did not observe a significant correlation between nitric oxide concentrations and semen profile.