Background and study aim: Rectal carcinoids are low-grade malignancies that are usually treated by endoscopic resection. However, on pathologic examination, resection margins that are positive for carcinoid cells are frequently found. Patient outcomes were reviewed after endoscopic resection of rectal carcinoids and the clinical significance of possible residual disease, as defined by pathologic and endoscopic examination, was evaluated. Patients and methods: The medical records and endoscopic findings of 347 patients presenting with rectal carcinoids to 14 university hospitals in Korea between January 1999 and June 2007 were retrospectively analyzed. Results: A total of 304 patients were treated with endoscopic resection, and 43 patents were treated with surgery. In the endoscopic resection group, the complete resection rate was 88.2% based on endoscopic appearance (CR-E) and 60.2% based on pathologic evaluation (CR-P). The agreement between CR-E and CR-P was low (=0.192). No residual tumors were found in 77 of 85 patients (90.6%) who were CR-E but not CR-P and who had endoscopic biopsy taken at 24-month follow-up. The receiver-operating characteristic curve identified an optimal cut-off value of 10.5mm, at which the sensitivity and the specificity for metastasis were 100% and 89%, respectively. The risk factors for metastasis by multivariate analysis were tumor size, increased mitotic rate, and lymphovascular invasion. Conclusions: Endoscopic resection is a safe and effective modality for treating well-differentiated rectal carcinoids smaller than 10mm in diameter. Discrepancies were observed between CR-E and CR-P. The risk factors for metastasis were tumor size, increased mitotic rate, and lymphovascular invasion.