BACKGROUND AND STUDY AIMS: The propriety of cold forceps polypectomy (CFP) using jumbo biopsy forceps for diminutive polyps remains controversial. We conducted a prospective study to evaluate the complete CFP resection rate of 3-5-mm polyps using additional endoscopic mucosal resection (EMR) specimens following CFP. PATIENTS AND METHODS: Patients with 3-5-mm protruded or flat elevated colorectal polyps diagnosed endoscopically as adenomas or serrated lesions were prospectively enrolled. CFP using jumbo biopsy forceps was used to remove the eligible polyps and repeated until the absence of residuals were confirmed via image-enhanced endoscopy or chromoendoscopy. After CFP, saline was injected at the defect, and the marginal specimen of the defect was resected using EMR to histologically evaluate the residue. The primary outcome was the complete CFP resection rate, which was defined as no residue at the EMR site. Other outcomes were the number of CFP bites and the complete resection rate by lesion size. RESULTS: Eighty patients with 120 polyps were enrolled. The mean polyp size was 4.1 ± 0.7 mm. The overall complete resection rate was 96.7% (95% confidence interval [CI], 91.7-98.7), and the rates for 3-, 4- and 5-mm polyps were 100% (95% CI, 86.7-100), 96.0% (95% CI, 86.5-98.9) and 95.5% (95% CI, 85.1-98.8), respectively. The one-bite CFP rates were 92%, 60% and 31% for the 3-, 4- and 5-mm polyps, respectively. CONCLUSIONS: The complete CFP resection rate for 3-5-mm polyps was acceptable, although the one-bite clearance rate decreased as the polyp size increased (UMIN000028841).