The long-term risks of colorectal cancer (CRC) and CRC-related death following adenoma removal are uncertain. Data are needed to inform evidence-based surveillance guidelines, which vary in follow-up recommendations for some polyp types. Using data from a large, community-based integrated health care setting, we examined the risks of CRC and related death by baseline colonoscopy adenoma findings.Participants at 21 medical centers underwent baseline colonoscopies from 2004 through 2010; findings were categorized as no adenoma, low-risk adenoma, or high-risk adenoma. Participants were followed until the earliest of CRC diagnosis, death, health plan disenrollment, or December 31, 2017. Risks of CRC and related deaths among the high- and low-risk adenoma groups were compared with the no adenoma group using Cox regression adjusting for confounders.Among 186,046 patients, 64,422 met eligibility criteria (54.3% female; mean age, 61.6±7.1 y; median follow-up time, 8.1 y from the baseline colonoscopy). Compared with the no-adenoma group (45,881 patients), the high-risk adenoma group (7563 patients) had a higher risk of CRC (hazard ratio [HR], 2.61; 95% CI, 1.87-3.63) and related death (HR, 3.94; 95% CI, 1.90-6.56), whereas the low-risk adenoma group (10,978 patients) did not have a significant increase in risk of CRC (HR, 1.29; 95% confidence interval, 0.89-1.88) or related death (HR, 0.65; 95% CI, 0.19-2.18).With up to 14-years of follow-up, high-risk adenomas were associated with an increased risk of CRC and related death, supporting early colonoscopy surveillance. Low-risk adenomas were not associated with a significantly increased risk of CRC or related deaths. These results can inform current surveillance guidelines for high- and low-risk adenomas.