For a study, researchers sought to summarise and analyze the outcomes of completion surgery, as well as to conduct a comparison with primary rectal resections. They chose all studies that reported any outcome of completion surgery after transanal local excision of early rectal cancer. Case reports, benign lesion studies, and studies using flexible endoscopic techniques were not included. After transanal local excision of early rectal cancers, the intervention was total mesorectal excision. The primary outcome measures were histopathological and long-term oncological outcomes of total mesorectal excision. Short-term perioperative outcomes were used as secondary outcome measures. The eligibility criteria were met by 23 studies involving 646 patients, and 8 studies were included in the meta-analyses. When compared to primary resections, patients undergoing completion surgery have longer operative times (standardised mean difference, 0.49; 95% CI, 0.23–0.75; P=0.0002) and more intraoperative blood loss (standardised mean difference, 0.25; 95% CI, 0.01–0.5; P=0.04), but perioperative morbidity was comparable (risk ratio, 1.26; 95% CI, 0.98–1.62; P=0.08). Completion surgery was associated with a higher rate of incomplete mesorectal specimens (risk ratio, 3.06; 95% CI, 1.41–6.62; P=0.005) and lower lymph node yields (standardized mean difference, –0.26; 95% CI, –0.47 to 0.06; P=0.01). Long-term outcome comparisons were limited, but no evidence of lower recurrence or survival rates was found. Only small retrospective cohort and case-control studies had been published on this topic, with significant heterogeneity limiting meta-analysis effectiveness. This review found insufficient long-term results to satisfy concerns about oncological safety and provides the strongest evidence that completion surgery was associated with an inferior histopathological grade of the mesorectum. Noninferiority must be demonstrated through international collaborative research.