Recent studies have shown that the sentinel lymph node (SLN) procedure might improve staging in colon cancer. However, low SLN identification and high false negative rates have also been reported. In a two-institution study, the SLN procedure with isosulfan blue 1% was performed according to a standardized protocol in 31 patients with open resections for colon cancer. Data were collected prospectively. The database was analyzed retrospectively to determine factors contributing to a low identification rate. The SLN identification rate was 87% and the false negative rate was 50%. Successful SLN identification was significantly associated with application of higher volumes of dye relative to the tumor diameter ( p = 0.04) and more frequent tumor localization in the sigmoid colon ( p = 0.04) as compared to missing SLN identification. The tumor diameter was not significantly different in the two groups. Sentinel lymph node identification in colon cancer depends on the amount of dye injected relative to the tumor size. Application of only 1 ml of dye-the amount generally recommended in the literature-is not sufficient in large tumors.