The management of patients with invasive carcinoma removed by colonoscopic polypectomy remains controversial. In order to assess the criteria for subsequent surgery after polypectomy, the histologic findings and outcome of 25 patients with invasive carcinomas treated by polypectomy were analyzed. Subsequent surgery was indicated when removed invasive carcinoma showed at least one of the following findings: 1) carcinoma near the surgical margin, 2) vessel invasion, 3) massive invasion, and 4) poorly differentiated adenocarcinoma. The authors considered those findings to be a risk factor for local residual carcinoma or lymph-node metastases, or both. Of 25 patients, 18 showed risk factors, with 16 receiving surgery. Only one had residual carcinoma in the lymphatic vessel of the surgical specimen. The remaining 15 had no carcinoma in the surgical specimens, however, one died of recurrent disease 55 months later. Two patients with risk factors received no surgery for various reasons. Local recurrent carcinoma developed in one 39 months later and the other had no recurrent carcinoma at autopsy. Seven patients without risk factors were adequately treated by polypectomy without recurrent disease 34 to 96 months later (average, 69 months). Consequently, of 18 patients with risk factors, 3 showed either residual carcinoma in the surgical specimens or recurrent carcinoma was found later. None of 7 patients without risk factors developed recurrent disease. We recommend that patients with risk factors be followed by surgery; however, patients without risk factors can be adequately treated by polypectomy alone.