538 Background: The benefits of laparoscopic surgery (LAP) in comparison with open surgery (OP) have been suggested; however, the long-term survival after LAP for advanced colorectal cancer (CRC) requiring complete mesocolic excision is still unclear. We conducted a study to confirm the non-inferiority of LAP to OP in terms of overall survival with less frequent post-operative morbidity. The primary analysis is planned in 2014, and short-term outcomes including post-operative complications are presented here. Methods: Only accredited surgeons from 30 Japanese institutions participated. Eligibility criteria included histologically proven CRC; tumor located in the cecum, ascending, sigmoid or rectosigmoid colon; T3 or deeper lesion without involvement of other organs; N0–2 and M0; tumor size =<8 cm; patient age 20-75 years. Patients were randomized preoperatively by the minimization method. Patients with pathological stage III received adjuvant chemotherapy with fluorouracil plus leucovorin. The primary endpoint is overall survival, and the planned sample size was 1050. Results: A total of 1057 patients were randomized (OP: 528, LAP: 529) between October 2004 and March 2009. Patients assigned to LAP had less blood loss than those assigned to OP (median 30 ml vs 85 ml, p<0.001), although LAP lasted 52 minutes longer than OP (p<0.001). Radicality of resection, as assessed by the number of resected lymph nodes, did not differ between the two groups. LAP was associated with earlier recovery of bowel function (p<0.001), and with a shorter hospital stay (p<0.0001) than OP. Morbidity and mortality until discharge did not differ between the two groups, except for fewer wound-related complications in LAP (p=0.007). Conclusions: Short-term clinical benefits of LAP were demonstrated, and laparoscopic surgery for advanced CRC can be performed safely by experienced surgeons. If the non-inferiority of LAP in overall survival is demonstrated in the primary analysis planned in 2014, LAP will be the new standard surgical procedure for CRC.