Background:When colonic adenoma involves diverticulum,inflammation in the diverticulum will increase the risk of adenomatous dysplasia.Therefore,patients with colonic diverticulum adenoma are at a higher risk of colon cancer,and the adenoma needs to be resected to avoid poor outcome and improve prognosis.Aims:To explore the efficacy and safety of endoscopic mucosal resection(EMR)in treatment of colonic diverticulum adenoma.Methods:Fourteen consecutive cases of colonic adenoma near or involving a diverticulum treated by EMR from Jun.2018 to Jan.2022 at the First People's Hospital of Hangzhou Lin'an District were collected,and their clinical characteristics and outcomes were analyzed.The primary outcome was complications,including bleeding,perforation,and electrocoagulation syndrome,while the secondary outcomes were the en bloc resection rate,complete resection rate and local recurrence rate.Results:Among the 14 patients with colonic diverticulum adenoma,13 were type A(near a diverticulum)while 1 was type B(involving a diverticulum).The diameter of the lesion was(0.76±0.25)cm,and the operation time was(19.67±5.33)minutes.The main histological type was tubular adenoma,and the pathological results was intraepithelial neoplasia in most of the cases.Delayed hemorrhage was observed in 1 patient(7.1%),and electrocoagulation syndrome in 1 patient(7.1%).No perforation event occurred.The en bloc resection rate and complete resection rate were 100%.Ten patients accepted reexamination of colonoscopy within 1 year after surgery,and no local recurrence was found.Conclusions:EMR is safe and effective for treatment of colonic diverticulum adenoma.However,patients using antiplatelet drugs and adenoma involving both appendiceal orifice and diverticulum should be alert to postoperative complications.