Purpose This study examined, at second-look arthroscopy, the results of open-wedge high tibial osteotomy (HTO) focusing on root tear of the medial meniscus posterior horn (RTMMP). Methods Among 31 consecutive patients who underwent HTO without a meniscectomy or pullout repair for RTMMP, 20 patients were available for second-look arthroscopic evaluation. All patients had medial unicompartmental arthritis. The healing status of the RTMMP was classified as complete, incomplete, and no healing. The difference in the weight bearing line from presurgery to the last follow-up was evaluated. Osteoarthritis and chondral lesions were evaluated, as were clinical results. Correlations between healing status and other variables (weight bearing line, cartilage status, and clinical scores) were assessed. The healed (10 patients) and nonhealed (incomplete 6 patients + no healing 4 patients) groups were also evaluated with respect to other variables. Results There were 10 (50%) cases with complete healing, 6 (30%) with incomplete healing, and 4 (20%) with no healing. Kellgren-Lawrence grade did not improve according to the standing plain radiograph ( P = .09). Progression of chondral lesions was not observed at second-look arthroscopy; some improvement was even observed ( P = .002). The median Lysholm score improved from 58 preoperatively to 88.5 at the last follow-up. The median Hospital for Special Surgery (HSS) score also increased significantly from 62.4 (range, 50 to 76) to 87.2 (range, 80 to 92; P = .003). The comparison between healed and nonhealed groups revealed no statistical differences in all variables. Conclusions This study revealed a high rate of healing of RTMMP after HTO without attempted repair. Healing of the meniscus was not associated with an improved clinical outcome. Level of Evidence Level IV, therapeutic case series.