Varicocele is a common finding in men.Varicocele correction has been advocated for young patients with testicular hypotrophy,but there is a lack of morphofunctional follow-up data.We assessed whether percutaneous treatment of left varicocele is associated with testicular “catch-up growth” in the following 12 months by retrospectively reviewing data from an electronic database of 10 656 patients followed up in our clinic between 2006 and 2016.We selected all young adults (＜35 years) with left varicocele who underwent percutaneous treatment,had a minimum of 12 months\' ultrasound imaging follow-up,and had no other conditions affecting testicular volume.One hundred and fourteen men (mean±standard deviation [s.d.] of age:22.8 ± 5.4 years) met the inclusion and exclusion criteria.Left testicular hypotrophy (LTH),defined as a ＞20％ difference between left and right testicular volume at baseline,was observed in 26 (22.8％) men.Participants with LTH (mean±s.d.:14.5 ± 2.7 ml) had lower baseline testicular volume compared to those without LTH (mean±s.d.:15.7 ± 3.8 ml;P =0.032).Repeated measures mixed models showed a significant interaction between LTH and time posttreatment when correcting for baseline left testicular volume (β =0.114,95％ confidence interval [CI]:0.018-0.210,P =0.020),resulting in a catch-up growth of up to 1.37 ml per year (95％ Cl:0.221-2.516).Age at intervention was also associated with reduced testicular volume (-0.072 ml per year,95％ CI:-0.135-0.009;P=0.024).Percutaneous treatment of left varicocele in young adults with LTH can result in catch-up growth over 1 year of follow-up.The reproductive and psychological implications of these findings need to be confirmed in longer and larger prospective studies.