Carcinoembriogenic antigen (CEA) is a routine marker for follow-up of colo-rectal cancers. We aimed to determine whether a CEA increase within the normal range can be linked to a recurrence risk. We included 78 consecutive patients with colo-rectal cancer, who underwent curative surgical treatment with or without chemo- or radiotherapy. As reference, we used the smallest value of the CEA during follow-up. A total of 34/78 patients (43.6%) had fluctuations of CEA of at least 1.1 ng/ml, with or without increases above 5 ng/ml. In 27/34 patients (79.4%) increases of CEA were explained either by recurrence (15/34 patients, 44.1%), adjuvant chemotherapy (7/34 patients, 20.6%) or benign pathology (5/34 patients, 14.7%). In 5 of 22 recurrences (23%) a CEA increase of at least 1.1 ng/ml, but below 5 ng/ml preceded the clinical relapse by a median of 8 months (range 3-22 months). The 4-year disease-free survival was 89% in patients with postoperative CEA <2.5 ng/ml, and 55% in patients with CEA >2.5 ng/ml. CEA increase by at least 1.1 ng/ml within the normal range, after curative treatment of colorectal cancer can be either an early sign of relapse or can be usually explained by other pathological processes.