ObjectiveTo explore the risk factors for unplanned readmission within 30 d after discharge in patients with colorectal cancer (CRC). MethodsClinical data were retrospectively collected from patients who underwent radical surgery for CRC in the Department of Gastrointestinal Surgery, The First Hospital of China Medical University, from January 2020 to December 2023. The data included demographic characteristics, Nutritional Risk Screening 2002 score, tumor characteristics, preoperative comorbidities, surgical and postoperative recovery status, and pre-discharge laboratory indicators. Univariate and multivariate logistic regression analyses were used to identify independent risk factors for unplanned readmission within 30 days after discharge. ResultsA total of 1 080 patients were included in this study. The rate of unplanned readmission within 30 d after discharge was 4.3% (46/1 080). The top three causes of unplanned readmission were postoperative ileus [50.0% (23/46)], infected peritoneal effusion [26.1% (12/46)], and gastrointestinal bleeding [8.7% (4/46)]. Multivariate analysis showed that rectal cancer [OR (95%CI)=2.773 (1.374, 5.594), P=0.004], stoma creation [OR (95%CI)=2.261 (1.184, 4.391), P=0.013], and preoperative hypoalbuminemia [OR (95%CI)=2.039 (1.097, 3.787), P=0.024] were independent risk factors for unplanned readmission within 30 d after discharge, while shorter time to first postoperative oral intake was a protective factor [OR (95%CI)=0.881 (0.99, 0.971), P=0.011]. ConclusionsThis study suggests that patients with rectal cancer, those underwent stoma creation, those with preoperative hypoalbuminemia, and those with delayed postoperative oral intake are at higher risk of unplanned readmission within 30 days after discharge. Perioperative management should be strengthened, including preoperative nutritional support, early postoperative oral intake, and stoma care, to reduce the risk of readmission.