Abstract Cold snare polypectomy (CSP), for the treatment of colorectal polyps, has become widespread due to its low incidence of adverse events compared to that of endoscopic procedures such as endoscopic mucosal resection. However, we experienced a case of large hematoma development shortly after CSP for a colorectal adenoma despite no bleeding during the procedure. The patient underwent CSP for a 7‐mm type Isp lesion in the ascending colon. She returned the following day because of hematochezia. Computed tomography showed a 70‐mm, high‐intensity mass in the ascending colon, consistent with the large hematoma that was detected by colonoscopy. Although the patient initially had right‐sided abdominal pain, it gradually improved with conservative treatment. The hematoma decreased in size, and she was discharged 20 days after emergency admission. Although CSP can be a favorable alternative to more invasive procedures and is expected to be performed more frequently, adverse events, such as that described in this case, should be anticipated.
