Although attempts have been made in the past to establish consensus regarding the definitions and grading of the severity of colorectal anastomotic leakage, widespread adoption has remained limited. A systematic review of the literature was conducted with the objective of examining the various elements used to report and define anastomotic leakage in colorectal cancer resections. A systematic review, using the PubMed, Embase, and Cochrane Library Database, of all published randomized controlled trials, systematic reviews, and meta-analyses containing data related to adult patients undergoing colorectal cancer surgery and reporting anastomotic leakage as a primary or secondary outcome, with a definition of anastomotic leakage included. Definitions of anatomotic leakage, clinical symptoms, radiological modalities and findings, findings at reoperation, as well as grading terminology or classifications for anastomotic leakage. Of the 471 articles reporting anastomotic leakage as a primary or secondary outcome, a definition was reported in 95 studies (45 randomized controlled trials, 13 systematic reviews, and 37 meta-analyses), involving a total of 346,140 patients. Of these 95 articles, 68% reported clinical signs and symptoms of anastomotic leakage, 26% biochemical criteria, 63% radiological modalities, 62% radiological findings, and 13% findings at reintervention. Only 45% (n = 43) of included studies reported grading of anastomotic leakage severity or leak classification, and 41% (n = 39) included a timeframe for reporting. There was a high heterogeneity between the included studies. This evidence synthesis confirmed incomplete and inconsistent reporting of anastomotic leakage across the published colorectal cancer literature. There is a great need for the development and implementation of a consensus framework for defining, grading, and reporting anastomotic leakage. Prospectively registered at PROSPERO ID 454660.