The present study aimed to assess the efficacy of surgery and adjuvant therapy in older patients (age≥70 years) with colorectal cancer (CRC). Older CRC patients are under-represented in available clinical trials, and therefore their outcomes after receiving surgery and adjuvant therapy are unclear. From two prospective Swedish databases, we assessed a cohort of 1021 patients who underwent curative surgery for stage I, II, or III primary CRC, with or without adjuvant chemotherapy/radiotherapy. Of the patients with colon cancer (n=467), 182 (39%) were aged <70 years, 162 (35%) aged 70 to 80 years, and 123 (26%) were aged ≥80 years. Of rectal cancer patients (n=554), 264 (48%) were aged <70 years, 234 (42%) aged 70 to 80 years, and 56 (10%) aged ≥80 years. Older patients with either colon or rectal cancer had higher comorbidity than did younger patients. Older patients with colon cancer had equivalent postoperative morbidity and 30-day mortality to younger patients. Rectal cancer patients aged ≥80 years had a higher 30-day mortality than younger patients (odds ratio [OR], 2.37; 95% confidence interval [CI], 1.6-4.55; P=0.03). For either colon or rectal cancer, adjuvant chemotherapy compromised the 5-year overall survival (OS) of older patients with stage II disease and had no effect on those with stage III disease. Receiving adjuvant chemotherapy was a poor factor of OS for older patients with either colon (HR 1.88, 95% CI: 1.20-4.35, P=0.03) or rectal cancer (HR 1.72, 95% CI: 1.05-2.26, P=0.004). Preoperative short-course radiotherapy improved both OS and local control for older patients with stage III rectal cancer and had no effect on those with stage II disease. Radiotherapy was a favorable factor for the OS of the older patients with rectal cancer (HR 0.42, 95% CI: 0.21-3.57, P=0.01). In conclusion, Older CRC patients had equal safety of surgery as younger patients, except rectal cancer patients aged ≥80 years that had a higher mortality. Adjuvant 5FU-based chemotherapy did not benefit older CRC patient, while neoadjuvant radiotherapy improved the prognosis of older patients with stage III rectal cancer.