Background Primary anastomosis (PA) in left-sided colorectal cancer (CRC) surgery in elderly patients is disputed. The aim of our study was to evaluate the differences in postoperative outcomes after left-sided CRC surgery in elderly patients in The Netherlands, comparing patients with PA and those who underwent end-ostomy (EO). Method Patients aged >= 75 years with stage I-III left-sided CRC, diagnosed and surgically treated in 2015-2017 were selected from the Netherlands Cancer Registry (n = 3286). Postoperative outcomes, short-term (30-, 60-, and 90-day) mortality and 3-year overall and relative survival were analyzed, stratified by surgical resection with PA versus EO. Propensity score matching (PSM) and multivariable logistic regression analysis were conducted. Results Patients with higher age, higher American Society of Anesthesiologists classification and higher tumor stage, a perforation, ileus or tumor located in the proximal rectum, and after open or converted surgery were more likely to receive EO. No difference in anastomotic leakage was seen in PA patients with or without defunctioning stoma (6.2% vs. 7.0%, p = 0.680). Postoperative hospital stay was longer (7.0 vs. 6.0 days, p < 0.0001) and more often prolonged (19% vs. 13%, p = 0.03) in EO patients. Sixty-day mortality (2.9% vs. 6.4%, p < 0.0001), 90-day mortality (3.4% vs. 7.7%, p < 0.0001), and crude 3-year survival (81.2% vs. 58.7%, p < 0.0001) were significantly higher in EO patients, remaining significant after multivariable and PSM analysis. Conclusion There are significant differences between elderly patients after left-sided CRC surgery with PA versus EO in terms of postoperative length of stay, short-term survival, 3-year overall survival, and relative survival at disadvantage of EO patients. This information could be important for decision making regarding surgical treatment in the elderly.