Background: There is an increasing incidence of neuroendocrine tumors (NET) of the colon and rectum likely related to increased screening colonoscopy and availability of better diagnostics. Most of these tumors identified during screening are low grade early-stage tumors with high cure rates. Data on long term risk of recurrence of NET and other second cancers is lacking. We studied the incidence rates of all second malignancies in survivors of NET of the colon and rectum. Methods: We analyzed data from the Surveillance, Epidemiology and End Results (SEER), Research Data 17 Registries, Nov 2022 Sub (2000-2022) to determine the risk of second malignancies in patients with an initial cancer diagnosis of NET of the colon and rectum. With these criteria we had overall 17,907 patients and 157,720 patient years of follow up. The relative risk of subsequent malignancies is reported as a standardized incidence ratio (observed incidence [O]/expected incidence [E]). Incidence ratios are analyzed over time from initial diagnosis to assess long term risk. Results: Survivors of NET of the large intestine are at highest risk of malignancy of the rectum (O/E: 6.4, CI: 7.26 - 5.61, N= 239) and this increased risk of rectal cancer persists even 10 years after the initial diagnosis (0/E: 3.8, CI: 5.37- 2.6, N= 32). There is no increased risk of cancer of the colon excluding rectum (O/E: 0.98, CI: 1.18-0.81, N= 114). Even after 10 years from diagnosis there is increased risk of second cancers for NET of the Colon (O/E: 1.28, CI: 1.55-1.06, N=110) and NET of the Rectum (O/E: 1.12, CI: 1.23- 1.02, N= 433). There is also increased incidence of small intestine cancer (O/E: 2.92, CI: 4.17- 1.97, N=30), Prostate cancer (O/E: 1.28, CI: 1.41- 1.15, N=400), Kidney and renal pelvis cancer (O/E: 1.53, CI: 1.86 -1.25, N= 104), Thyroid cancer (O/E: 1.63, CI: 2.12-1.23, N= 55) and Nodal Non-Hodgkins Lymphoma (O/E: 1.34, CI: 1.71-1.03, N=64). Conclusions: Survivors of NET of the large intestine are at risk of developing subsequent malignancies. The information presented may help physicians in effectively monitoring survivors for second cancers at various timeframes from their initial diagnosis.