PURPOSE: The aim of this study is to assess effects of testicular volume difference and retrograde venous flow of pampiniform plexus measured by Duplex Doppler Ultrasonograpy (DDU) in patients with adolescent varicocele. MATERIALS AND METHODS: Physical examinations and DDU were performed to assess varicocele in fifty five patients with left sided adolescent varicocele. During both normal respiration and the Valsalva's maneuver, the maximum venous diameter (MVD), maximal velocity of reflux and the peak retrograde flow volume (RFV) was measured by DDU. The percentage testicular volume difference (%) between the right and left testicle was calculated as (right testicular volume-left testicular volume)x100/right testicular volume and divided into 3 group; below 10%, 10~20%, >20%. Grade of varicocele, MVD and peak RFV were analyzed as possible determinants of testicular hypotrophy in adolescent varicocele. RESULTS: A total of 55 patients (mean age 17.8 years, range 12 to 20) were included in this study. Of these, physical examination reviewed that 7 (12.7%), 18 (32.7%), 30 (54.6%) patients had grade I, II or III varicoceles on the left side respectively. The mean MVD was significantly higher according to grade of varicocele. The mean maximal velocity of reflux was significantly higher in the patients grade II and III than grade I, but was not significant between grade II and III. The mean peak RFV was significantly higher according to grade of varicocele. RFV was the only significant parameter of predictive value for percentage testicular volume difference. CONCLUSIONS: Patients with peak RFV >35ml minutes showed significant reduction of testicular volume. Measurement of RFV is recommended as predictive tools for assessing the percentage testicular volume difference in patients with adolescent varicocele.