BACKGROUND: Reliable and modern information on primary evaluation, treatment, and long-term survival rates for patients with colorectal cancer (CRC) metastases are needed. Whether synchronous CRC metastases carry a worse prognosis than metachronous is still debated. METHODS: Population-based study on 7,950 CRC patients from Central Norway, 2001- 2015. Of these, 1,843 (23.2%) had synchronous metastases and of radically operated patients with stage I-III disease 1,117 (20.1%) developed metachronous metastases. The treatment strategies and outcomes for patients with metastases were analyzed, stratified by three consecutive 5-year periods. RESULTS: Median and 3-year survival for patients with synchronous metastases were 11 months and 16.4%, compared to 17 months and 29.4% with metachronous metastases, p < 0.001 and p < 0.001, respectively. The subsets receiving supportive care only, had a median survival of 3-4 months. Patients with synchronous metastases and primary palliative chemotherapy had a median survival of 15 months compared to 18 months with metachronous metastases, p < 0.001. Neither groups improved survival across the study period. The 5-year survival for the 342/1,843 (18.6%) patients with synchronous metastases and curative intent treatment was 41.8% compared to 43.6% for the corresponding 422/1,117 (37.8%) patients with metachronous metastases, log-rank p = 0.281. Survival significantly improved for both these groups across the study period. INTERPRETATION: A key determinant of better survival for patients with metachronous CRC metastases compared to synchronous was a significantly higher proportion treated with curative intent. Survival for both patients with synchronous and metachronous metastases taken collectively steadily improved during the study period, driven by the increased proportions and improved survival for the subsets with curative intent treatment.