Laparoscopic procedures are generally thought to have better outcomes than open procedures. Because of anatomical constraints, laparoscopic rectal resection may not be better because of limitations in performing an adequate cancer resection. To determine whether laparoscopic resection is noninferior to open rectal cancer resection for adequacy of cancer clearance. Randomized, noninferiority, phase 3 trial (Australasian Laparoscopic Cancer of the Rectum; ALaCaRT) conducted between March 2010 and November 2014. Twenty-six accredited surgeons from 24 sites in Australia and New Zealand randomized 475 patients with T1-T3 rectal adenocarcinoma less than 15 cm from the anal verge. Open laparotomy and rectal resection (n = 237) or laparoscopic rectal resection (n = 238). The primary end point was a composite of oncological factors indicating an adequate surgical resection, with a noninferiority boundary of Δ = -8%. Successful resection was defined as meeting all the following criteria: (1) complete total mesorectal excision, (2) a clear circumferential margin (≥1 mm), and (3) a clear distal resection margin (≥1 mm). Pathologists used standardized reporting and were blinded to the method of surgery. A successful resection was achieved in 194 patients (82%) in the laparoscopic surgery group and 208 patients (89%) in the open surgery group (risk difference of -7.0% 95% CI, -12.4% to ∞; P = .38 for noninferiority). The circumferential resection margin was clear in 222 patients (93%) in the laparoscopic surgery group and in 228 patients (97%) in the open surgery group (risk difference of -3.7% 95% CI, -7.6% to 0.1%; P = .06), the distal margin was clear in 236 patients (99%) in the laparoscopic surgery group and in 234 patients (99%) in the open surgery group (risk difference of -0.4% 95% CI, -1.8% to 1.0%; P = .67), and total mesorectal excision was complete in 206 patients (87%) in the laparoscopic surgery group and 216 patients (92%) in the open surgery group (risk difference of -5.4% 95% CI, -10.9% to 0.2%; P = .06). The conversion rate from laparoscopic to open surgery was 9%. Among patients with T1-T3 rectal tumors, noninferiority of laparoscopic surgery compared with open surgery for successful resection was not established. Although the overall quality of surgery was high, these findings do not provide sufficient evidence for the routine use of laparoscopic surgery. Longer follow-up of recurrence and survival is currently being acquired. anzctr.org Identifier: ACTRN12609000663257.