We previously demonstrated that false-positive findings for tumor markers are frequently observed, and that the sensitivity of marker monitoring for early detection of the recurrence is low after curative resection of gastric cancer. The aim of this study was to investigate whether such characters are specific to gastric cancer. Serum carcinoembryonic antigen and/or carbohydrate antigen 19–9 were periodically assessed in 258 patients who underwent curative gastrectomy for gastric cancer (n = 161) or curative resection for colorectal cancer (n = 97). The frequency of false-positive findings for the tumor markers, the sensitivity of the marker monitoring for detection of the recurrence, and the characteristics of such cases were compared between these two cancer groups. During the median follow-up period of 30 months, recurrence developed in 14% of gastric cancer and 23% of colorectal cancer patients. A false positive with the tumor marker was frequently observed in patients after gastrectomy compared with after colorectal surgery. The sensitivity of the marker monitoring regarding early detection of recurrence was higher in patients with colorectal cancer than those with gastric cancer, especially in cases of advanced stage. As a result, the accuracy of marker monitoring for the detection of recurrence was higher in patients after the resection of colorectal cancer than that of gastric cancer. Surgeons and oncologists should thus be aware that the role of the tumor marker monitoring after a curative operation differs between patients with gastric and colorectal cancers.