PURPOSE: We evaluated the impact of varicocele grade on the response to varicocelectomy or spermatic vein embolization. MATERIALS AND METHODS: We systematically reviewed the published English language literature to identify studies on changes in semen quality and pregnancy outcomes after varicocele treatment, stratified by varicocele grade. Descriptive statistics and continuous random effects models were used to study the impact of varicocele grade and the surgical approach on the response to treatment. Result heterogeneity among studies was analyzed using the I2 statistic. Quality assessment of nonrandomized studies was done with the Newcastle-Ottawa Scale. Publication bias was analyzed using funnel plots and the Egger test. RESULTS: We identified 20 studies describing the outcome of varicocele treatment stratified by varicocele grade in a total of 2,001 infertile men with varicocele. A microsurgical approach (inguinal, subinguinal and/or Palomo) was used in 11 of the 20 studies (55%). Varicocele treatment was associated with improvements in sperm concentration and overall motility in patients with all grades of varicocele. Semen quality improvements were directly related to varicocele grade. The mean sperm concentration improvement in men with grades 1, 2, 2-3 and 3 varicoceles were 5.5, 8.9, 12.7 and 16.0 million sperm per ml, respectively. The mean improvement in the percent of overall motility in men with grades 1, 2, 2-3 and 3 varicoceles was 9.6%, 10.6%, 10.8% and 17.7%, respectively. Pregnancy outcomes were assessed but could not be analyzed systematically due to the lack of adequate published data. CONCLUSIONS: Mean improvements in the sperm concentration and the percent of overall motility after treatment of grade 1 varicocele were statistically significant but small in magnitude. In contrast, mean improvements in the sperm concentration and the percent of overall motility after treatment of grade 2-3 varicoceles were greater and highly likely to be clinically significant. Incorporating varicocele grade into shared decision making discussions with affected couples may improve the ability to select patients who are the best candidates for treatment.