Background: We previously reported that in pathogenic mismatch repair (path-MMR) variant carriers, the incidence of colorectal cancer (CRC) was not reduced when colonoscopy was undertaken more frequently than once every 3 years, and that CRC stage and interval since last colonoscopy were not correlated. Methods: The Prospective Lynch Syndrome Database (PLSD) that records outcomes of surveillance was examined to determine survival after colon cancer in relation to the time since previous colonoscopy and pathological stage. Only path-MMR variants scored by the InSiGHT variant database as class 4 or 5 (clinically actionable) were included in the analysis. Results: Ninety-nine path-MMR carriers had no cancer prior to or at first colonoscopy, but subsequently developed colon cancer. Among these, 96 were 65 years of age or younger at diagnosis, and included 77 path-MLH1, 17 path-MSH2, and 2 path-MSH6 carriers. The number of cancers detected within < 1.5, 1.5-2.5, 2.5-3.5 and at > 3.5 years after previous colonoscopy were 9, 43, 31 and 13, respectively. Of these, 2, 8, 4 and 3 were stage III, respectively, and only one stage IV (interval 2.5-3.5 years) disease. Ten-year crude survival after colon cancer were 93, 94 and 82% for stage I, II and III disease, respectively (p < 0.001). Ten-year crude survival when the last colonoscopy had been < 1.5, 1.5-2.5, 2.5-3.5 or > 3.5 years before diagnosis, was 89, 90, 90 and 92%, respectively (p = 0.91). Conclusions: In path-MLH1 and path-MSH2 carriers, more advanced colon cancer stage was associated with poorer survival, whereas time since previous colonoscopy was not. Although the numbers are limited, together with our previously reported findings, these results may be in conflict with the view that follow-up of path-MMR variant carriers with colonoscopy intervals of less than 3 years provides significant benefit.