Relationships between the size of primary epidermoid carcinomas of the anal canal (ECAC) and the size, number and distribution of metastases to the lymph nodes (LNM) are not known. Reported herein are the results of a retrospective study of 29 patients who underwent potentially curative abdominoperineal resections for ECAC and whose surgical specimens were treated by a clearing technique of the lymph nodes. Five of 16 patients with stage T3 or larger lesions and one patient of 11 with T2 or smaller lesions had LNM (p less than 0.05). Forty-four per cent of the LNM were found in lymph nodes measuring less than 5 millimeters in diameter. Analysis of maps of lymph nodes allowed us to observe that most lymph nodes are located above the peritoneal reflection, that lymph nodes are scant in the perianal zone, that the perirectal zone contains an average of nine lymph nodes and that LNM are most common in the perirectal zone. A lack of association between the size of primary ECAC and LNM is noted, and metastases to small lymph nodes (less than 5 millimeters) are found to be a common occurrence. This may explain previous understaging of patients.