Purpose <p>Compare clinical outcomes between type I endoscopic over-underlay tympanoplasty (EOUT) and type I endoscopic overlay tympanoplasty (EOT) for repairing medium-to-large-sized tympanic membrane perforations.</p> Methods <p>A prospective, single-blind, randomized controlled trial was conducted at a single tertiary university hospital involving 46 patients (aged 18–75 years) between September 2023 and July 2024. All patients had a persistent dry middle ear status for more than three months and underwent endoscopic tympanoplasty. The primary outcomes were graft success rate and hearing improvement, while the secondary outcomes included operative time and postoperative complications.</p> Results <p>A total of 43 patients were analyzed (EOUT, 22; EOT, 21). The overall graft success rate was 95.3%, with no significant intergroup differences (EOUT, 95.5% vs. EOT, 95.2%; <i>p</i> = 0.999). Postoperative pure-tone average air conduction threshold improved significantly in both groups (EOUT: from 39.03 ± 13.62 dB to 27.84 ± 11.72 dB; EOT: from 36.13 ± 14.26 dB to 25.00 ± 12.53 dB; <i>p</i> &lt; 0.001). Similarly, the air-bone gap improved (EOUT: from 13.47 ± 7.20 dB to 4.26 ± 3.33 dB; EOT: from 12.32 ± 8.33 dB to 3.87 ± 3.93 dB; <i>p</i> &lt; 0.001). Mean operative times were comparable (EOUT: 102.45 ± 13.04&#xa0;min vs. EOT: 104.29 ± 15.43&#xa0;min; <i>p</i> = 0.676), without postoperative hearing deterioration.</p> Conclusion <p>EOUT and EOT appear to be effective techniques for repairing medium-to-large-sized tympanic membrane perforations, showing high graft success rates and significant audiological improvements, with no statistically significant differences observed between the techniques. These findings are promising and may support future studies with larger sample sizes and longer follow-up periods.</p> Clinical trial registration <p>Prospectively registered– Thai Clinical Trials Registry (TCTR) under TCTR20230911001 on 11 September 2023.</p>