The clinical courses of 64 patients undergoing abdominoperineal resection for Stage I lower rectal carcinoma (tumors confined to the muscularis propria without lymph node involvement) were reviewed to identify subsets at risk for failure. Twelve of 12 patients with tumors limited to the submucosa remained disease free without evidence of recurrence. Of the 52 patients with muscularis propria involvement, there have been eight failures with three patients having local failure only, three patients with local failure and distant metastases, and two patients with distant metastases only. The 6-year actuarial disease-free survival, local control, and freedom from distant metastases rates for patients with tumors invasive of the muscularis propria were 80%, 84%, and 88%, respectively. Patients with tumors exhibiting vascular/lymph vessel involvement were at even higher risk for failure. Although adjuvant treatment is infrequently advised for these patients, the use of radiation therapy and chemotherapy should be reconsidered for patients with Stage I lower rectal carcinoma, specifically for patients with tumors invasive of the muscularis propria with vascular/lymph vessel involvement.