OBJECTIVES: The aims of this prospective study were to document the incidence of colon immediate postpolypectomy bleeding (IPPB) according to grade, and to identify potential risk factors of IPPB in patients who have received complete colonoscopy and polypectomy because of a colorectal polyp. METHODS: This was a prospective, cross-sectional study of 5,152 patients treated at 11 tertiary medical centers between July 2003 and July 2004. Patient-related, polyp-related, and procedure-related variables were evaluated as potential risk factors for IPPB. IPPB was defined as a bleeding occurring during the procedure and was graded as G1-G4. Risk factors associated with IPPB were analyzed by univariate and multivariate logistic regression analysis. RESULTS: A total of 9,336 colonic polyps were removed in 5,152 patients, and 262 (2.8%) colorectal polyps in 215 patients presented with IPPB. Polyp-based multivariate analysis revealed that old age (≥65 yr), comorbid cardiovascular or chronic renal disease, anticoagulant use, polyp size greater than 1 cm, gross morphology of polyps such as pedunculated polyp or laterally spreading tumor, poorer bowel preparation, cutting mode of the electrosurgical current, and the inadvertent cutting of a polyp before current application were significant risk factors for IPPB. CONCLUSION: Nine factors have been found to be associated with IPPB and polypectomy should be undertaken with caution under these conditions.