The incidence of metastases from primary adenocarcinoma of the rectum in lymph nodes smaller than 5 mm is not known. Lymph nodes measuring less than or equal to 5 mm usually are not detected by manual techniques of examination of the surgical specimen. This retrospective analysis describes the results when a lymph node clearing technique that identifies lymph nodes as small as 1 mm was used to treat surgical specimens from 27 consecutive patients with rectal adenocarcinoma who underwent abdominoperineal resection with a curative intent and for whom all pathologic data were retrievable. Nine hundred thirty lymph nodes were found, with an average of 34 lymph nodes per specimen (range 0-88). Seventy-two of the 345 lymph nodes found in patients with Dukes C tumors were found to have metastases. Fifty-six (78 percent) of these 72 lymph node metastases occurred in lymph nodes measuring less than or equal to 5 mm. Three lymph node metastases were found in the perianal zone, 53 in the perirectal zone, and 16 in the pericolonic zone. Lymph node metastases from rectal adenocarcinomas often will occur in lymph nodes smaller than 5 mm. We concluded that the use of lymph node clearing techniques discovers these metastases, thereby offering the potential for enhanced staging of primary rectal adenocarcinomas.