Background: Improvements in early detection and treatment have resulted in an increasing number of long-term survivors of colorectal cancer (CRC). For the survivors, Second primary cancers and recurrence are important issues, but the evidence for appropriate surveillance strategy is limited. The aim of this study was to investigate the frequency and the timing of second primary cancers and recurrence in patients (pts) after surgery using 3 randomized trials (J0205, J0212 and J0404) conducted by Colorectal Cancer Study Group of JCOG. Methods: Eligibility criteria included histologically proven CRC and having received surgery. The timing, site and frequency of second primary cancer and recurrence were investigated. Risk factors associated with the events were explored. Standardized incidence ratio (SIR) about second primary cancer compared with national database of Japan Cancer Registry was estimated. Results: A total of 2,824 pts with a median follow-up time of 6 years were included. Median age was 62 years old (23-75), male/female was 58%/42%, and stage 0/I/II/III/IV was 0.2%/8.7%/25.4%/64.8%/0.9%. Pts with 5-FU based adjuvant chemotherapy were 63%. Cumulative incidence of second primary cancer increased constantly over time (Table). Among 240 pts, the most common site was lung (37), stomach (35) and colon (32). In multivariable analysis, age (over 64 years old) and sex (male) were risk factors (age HR: 1.60 (95% CI: 1.24-2.07), sex HR: 1.36 (95% CI: 1.04-1.78)). The SIR of any second primary cancers was 1.07 (95% CI: 0.94-1.21). The SIR for second primary cancers of colon was 1.09 (95% CI: 0.79-1.47). On the other hand, cumulative incidence of recurrence almost reached at 3 years. Conclusions: Common surveillance strategy can be applied even for curatively resected CRC pts after 3 years from surgery, because the risk of second primary cancer was almost same as general population over time. The necessity of intensive follow-up to detect recurrence decreases after 3 years.