OBJECTIVE To determine the relationship between renospermatic basal reflow at color Doppler ultrasound (CDU) evaluation and the improvement in seminal quality after sclerotization of varicocele, and the role of patients' age. No clear predictive factors are available for selecting patients who will show a better seminal improvement after varicocele correction. METHODS Between 2002 and 2008 we selected 113 patients with left unilateral varicocele, meeting the criteria of low sperm density, no endocrinological failures and no varicocele recidivating. Varicocele correction was performed using the retrograde sclerotization technique or, if not possible, the anterograde one. Patients underwent a physical examination, follicle-stimulating hormone assessment, sperm analysis (density, motility, and morphologic analysis), scrotal ultrasound, and CDU evaluation. Patients were divided into 5 groups using the CDU classification (Sarteschi). Three months postoperatively, they were assessed with the same protocol. Mean age was 32.2 years. RESULTS We found improvement in seminal quality among the entire population. We found no significance in differences among semen quality improvement in patients of different ages. Patients with basal renospermatic reflow at preoperative CDU evaluation (groups 3, 4, and 5) showed a better improvement in sperm density (+139%) than patients with no basal reflow (groups 1 and 2; +61%). CONCLUSIONS The presence of a basal reflow at preoperative CDU is a strong predictive factor of a better seminal quality improvement after varicocele correction. On the contrary, patient's age showed no significant relationship.