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BACKGROUND Short-course radiation therapy and consolidation chemotherapy with nonoperative intent has emerged as a novel treatment paradigm for patients with rectal cancer, but there are no data on the predictors of clinical complete response. OBJECTIVE To evaluate the predictors of clinical complete response and survival. DESIGN Retrospective cohort. SETTINGS NCI-designated cancer center. PATIENTS Stage I-III rectal adenocarcinoma treated between 01/2018 and 05/2019 (n = 86). INTERVENTIONS Short-course radiation therapy followed by consolidation chemotherapy. MAIN OUTCOME MEASURES Logistic regression were performed to assess for predictors of clinical complete response. The endpoints included local regrowth-free survival, regional control, distant metastasis-free survival, and overall survival. RESULTS A positive (+) circumferential resection margin by magnetic resonance imaging at diagnosis was a significant predictor of non-clinical complete response (odds ratio: 4.1, p = 0.009) when adjusting for carcinoembryonic antigen level and primary tumor size. Compared to patients with a negative (-) pathologic circumferential resection margin, patients with a positive (+) pathologic circumferential resection margin had inferior local regrowth-free survival (29% vs. 87%, p < 0.001), regional control (57% vs. 94%, p < 0.001), distant metastasis-free survival (43% vs. 95%, p < 0.001), and overall survival (86% vs. 95%, p < 0.001) at 2 years. However, the (+) and (-) circumferential resection margin by magnetic resonance imaging subgroups in patients who had a clinical complete response both had similar regional control, distant metastasis-free survival, and overall survival of >90% at 2 years. LIMITATIONS Retrospective design, modest sample size, short follow-up, and the heterogeneity of treatments. CONCLUSIONS Circumferential resection margin involvement by magnetic resonance imaging at diagnosis is a strong predictor of non-clinical complete response. However, patients who achieve a clinical complete response following short-course radiation therapy and consolidation chemotherapy with nonoperative intent have excellent clinical outcomes regardless of the initial circumferential resection margin status.