Although favorable results have been reported on catheter-directed sclerotherapy (CDS) for ovarian endometrioma, a thorough evaluation of its long-term efficacy is lacking. This study evaluates the long-term efficacy and safety of CDS with 99% ethanol for treatment of ovarian endometrioma. Between January 2020 and February 2022, data from 33 consecutive patients with symptomatic ovarian endometriomas who underwent CDS were retrospectively evaluated. All patients underwent pre-procedural and 6- and 12-month post-procedural ultrasonography. To assess the effect on ovarian reserve, serum anti-Müllerian hormone (AMH) levels were measured before and after the procedure. Procedure-related complications were also assessed. The mean volume of endometriomas decreased from 80.22 ± 66.43 to 0.73 ± 1.10 mL (P < 0.001), and the mean percentage of volume reduction was 98.99% ± 1.53%. No recurrences were observed during the follow-up period. In patients whose serum AMH levels were monitored for 1 year, no significant change in AMH level before and after CDS was observed (3.07 ± 1.81 vs. 2.72 ± 2.02 ng/mL, P = 0.190). One patient complained of moderate abdominal pain after CDS, which was conservatively managed. CDS remained safe and effective in treating ovarian endometrioma at the 1-year follow-up. Ovarian function after CDS was well preserved. CDS is a safe and effective treatment option for patients with ovarian endometrioma without compromising ovarian function.