OBJECTIVE To study youth who have a varicocele or are undergoing varicocele treatment, in relation to changes in semen, as measured by semen analysis (SA). METHODS Meta-analysis of studies identified via a search of PubMed, Medline, and the Cochrane Library covering the last 40 years. METHODS Not applicable. METHODS Youth from studies that assessed the presence and/or treatment of varicocele with SA. METHODS Selected studies were analyzed in two separate meta-analyses: one for the effect of varicocele on semen, as measured by SA (hypothesis #1), the other for the effect of treatment on semen, as measured by SA (hypothesis #2). METHODS A random-effects model was used to calculate weighted mean difference (WMD) of semen outcomes. Heterogeneity was calculated. Bias was assessed with funnel plots and Egger's test. RESULTS The initial literature search returned 1,180 potentially relevant articles. For hypothesis #1, 10 studies with a total of 357 varicocele and 427 control subjects were included. Sperm density, motility, and morphology were significantly decreased when associated with a varicocele, with a WMD of -24.0×10(6)/mL (95% confidence interval [CI; -39.5 to -8.6]), -7.5% (95% CI [-12.3% to -2.7%]), and -1.7% (95% CI [-2.4% to -1.1%]), respectively. Another 10 studies with 379 treated and 270 untreated subjects were analyzed for hypothesis #2. Sperm density and motility were significantly improved following treatment, with a WMD of 14.6×10(6)/mL (95% CI [7.1-22.1]) and 6.6% (95% CI [2.1%-11.2%]), respectively. CONCLUSIONS The presence of varicocele in youth appears to negatively affect sperm density, motility, and morphology. Treatment appears to result in moderate improvement of sperm density and mild improvement in sperm motility.