We retrospectively reviewed 76 cases of adenocarcinoma of the lower rectum treated by abdominoperineal resection between 1975 and 1985 to elucidate the relationship between pathologic stage and both the size and histologic grade of the tumor. Our results showed evidence of lymphatic invasion in 50% of the 36 patients with tumors 4.0 cm or less in diameter, 51% of the 68 patients with tumors of either a high or moderate degree of differentiation, and an alarming 53% of the 34 patients whose tumors satisfied both criteria simultaneously. Finally, a substantial proportion (25%) of patients who had only partial invasion of the muscular layer also had lymphatic metastases. These results differ significantly from what has been previously reported and lead us to conclude that the commonly used criteria of size and histologic grade are inadequate criteria and do not allow confident selection of patients with lesions suitable for local treatment.