Background and Aims: The aim of this study was to describe short-term changes in morbidity and mortality associated with the implementation of screening for colorectal cancer in Denmark. Materials and Methods: Prospective cohort study with inclusion of all patients aged 50–75 years treated for colorectal cancer between 1 March 2014 and 31 December 2015 in Denmark. Adjusted hazard ratios were calculated for 30 and 90 days mortality using Cox Regression. We made two adjusted models—a “basic” adjusted for screening status, sex, age, smoking, alcohol consumption, and cancer type and an “advanced” that also included body mass index and American society of Anesthesiologists score in analyses. Relative risks were calculated for postoperative surgical and medical complications. Results: In total, 5348 patients were included. In the “basic model,” adjusted risk of 30 and 90 days total mortality was reduced in the screen-detected group (p < 0.01, HR = 0.43, CI = 0.24–0.76) and (p < 0.01, HR = 0.45, CI = 0.30–0.69). In the “advanced model,” only 90 days total mortality was significantly reduced in the screen-detected group (p = 0.01, HR 0.59, CI = 0.39–0.90). No significant changes were found with regard to surgical and medical complications, respectively, (p = 0.05 (CI = 0.76–1.00) and p = 0.47(CI = 0.74–1.15)). Conclusion: This nationwide study showed that screening for colorectal cancer was associated with a lower 90 days total mortality although no significant improvements were seen with regard to morbidity.