OBJECTIVES: 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 wit