CONTEXT: The serum carcinoembryonic antigen (CEA) is an important prognostic factor in colorectal cancer, however the rectum presents different routes of venous drainage, stating that the level of CEA in peripheral and mesenteric rectal tumors may be different, depending on the location of the tumor in the rectal segment. OBJECTIVE: The goal of this study was to evaluate the relationship between the peripheral and mesenteric venous levels of CEA and the association between these levels and the tumour location in the rectums of patients successfully operated on for rectal carcinoma. METHODS: Thirty-two patients who were surgically treated for rectal carcinoma were divided into patients with tumours located in the upper rectum (n = 11) or lower rectum (n = 21). The CEA values were assessed by electrochemiluminescence immunoassay. Serum and mesenteric CEA levels were associated with the tumour anatomopathological characteristics: location, histological type, cellular differentiation grade, depth of invasion into the rectal wall, angiolymphatic invasion, tumour, node, and metastasis staging; and the CEA index (≤1.0 or ≥1.0 ng /mL). RESULTS: Analysis of the serum CEA values using clinical and anatomopathological parameters revealed no significant association with tumour location, histological type, cellular differentiation grade, depth of invasion into the intestinal wall, and tumour, node, and metastasis staging. The mesenteric CEA levels were significantly associated with the tumour location (P = 0.01). The CEA values in the mesenteric venous blood and the presence of angiolymphatic invasion (P = 0.047) were significantly different. A significant relationship was found between the CEA index value and the rectal tumour location (P = 0.0001). CONCLUSIONS: The CEA levels were higher in the mesenteric vein in tumours located in the upper rectum and in the presence of angiolymphatic invasion. CEA drainage from lower rectum adenocarcinomas preferentially occurs through the systemic pathway.