Background: In a portion of patients with DNA mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) rectal cancer, clinical complete response (cCR) could be achieved after anti-programmed cell death protein 1 (anti-PD-1) immuno-therapy. However, no data are available concerning the safety of omitting surgery and adopt-ing immunotherapy as a curative-intent treatment for these patients.Methods: We retrospectively collected a series of patients with dMMR/MSI-H rectal adeno-carcinoma who had cCR after receiving anti-PD-1 immunotherapy and adopted immuno-therapy as curative-intent treatment from six institutions. Survival outcomes were analysed using the Kaplan-Meier method.Results: Nineteen patients were included with a median age of 48 (range 19-63). One patient was diagnosed with stage I disease, four with stage II disease and fourteen with stage III disease. Sixteen patients received anti-PD-1 immunotherapy as the first line of therapy, and eleven patients were treated with single-agent anti-PD-1 antibodies. The median time from the start of treatment to cCR was 3.8 (range 0.7-6.5) months. During a median follow-up of 17.1 (range 3.1-33.5) months since achieving cCR, no local or distant relapse was observed. Two-year local recurrence-free survival, distant metastasis-free survival, disease free-survival and overall survival for the whole cohort were 100%, 100%, 100% and 100%, respectively.Conclusions: For patients with dMMR/MSI-H locally advanced rectal cancer who achieved cCR during anti-PD-1 immunotherapy, adopting immunotherapy as curative-intent treatment might be an alternative option. Longer follow-up and larger cohorts are warranted to verify this innovative treatment approach.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).