Correct determination of lymphatic nodal statement is necessary to stage accurately and to predict survival. As it is so critical to make an evaluation about the adjacent lymph node(s) this study was designed to make a sensitive detection on the sentinel lymph nodes (SLN) indicating tumoral lymphatic basin by using ultrastaging pathologic examination. From June 2002 to June 2003, this prospective study was performed in 46 patients undergoing standard resection for colorectal cancer. In this study, we employed the ex-vivo SLN mapping technique. At least one SLN in 37 of 41 patients was identified (90.2%). The lymph nodes (LN) from those patients were utilized by Hematoxylin and Eosin dye (H&E) and multisectioning. Then 20/37 patients with trace of the metastasis were found. Remaining 17 patients without any metastatic LN by H&E were applied to clarify micrometastases (MM) by using immunohistochemical (IHC) staining technique. 2 patients (11.7%) had MM in the SLN(s). Then upstaging was evaluated in those 2. The sensitivity of SLNs was obtained as 90%. Two patients with no metastatic SLN had metastasis in the non-sentinel LNs. MM in the SLN identified by IHC in the patients with CRC is still not obvious to display bad prognosis. But upstaging and the need for treatment alteration in those patients were obvious. [Turk J Cancer 2005;35(1):12-18].