Background and Aims <p>Growing evidence suggests that the gut microbiome plays a role in carcinogenesis for early-onset colorectal cancer (EOCRC). The novel Ring Finger Protein 213 (RNF213) gene has broad antimicrobial properties. Our study aimed to compare RNF213 mutation rates in EOCRC and late-onset colorectal cancer using data from the cBioPortal for Cancer Genomics.</p> Methods <p>All participants from the cBioPortal with CRC samples that profiled the RNF213 gene were included. Multivariable logistic regression was used to assess the association between EOCRC and primary tumor RNF213 mutation. Cox proportional hazards models were used to evaluate the influence of RNF213 mutation on all-cause mortality risk. All tests were two-sided.</p> Results <p>1594 participants with CRC from six cohorts were included, of which 7.8% (<i>N</i> = 125) had EOCRC. Participants with EOCRC were more likely to have late-stage CRC (<i>p</i> &lt; 0.001) and left-sided tumors (<i>p</i> &lt; 0.001). Participants with a mutation in exon 29 of RNF213 had significantly increased odds of EOCRC diagnosis (_adjOR 3.82, 95% CI 1.82, 7.54) compared to participants with wild-type RNF213, while mutations in other exons did not confer significantly increased odds of EOCRC diagnosis (_adjOR 1.61, 95% CI 0.72, 3.22). There was no significant difference in all-cause mortality risk by RNF213 mutation status.</p> Conclusions <p>Primary tumor mutations in exon 29 of the RNF213 gene are associated with significantly increased odds of EOCRC diagnosis in a multicohort sample of participants with CRC. Future studies of germline and precancerous RNF213 mutations are needed to elucidate its possible role in EOCRC tumorigenesis.</p>