Encouraging results from our previous studies of sentinel lymph node (SLN) mapping in colorectal cancer (CRC) prompted investigation of its feasibility and accuracy during laparoscopic colectomy for early CRC. Between 1996 and 2000, 14 patients with clinically localized colorectal neoplasms underwent colonoscopic tattooing of the primary site and SLN mapping. In each case 0.5 to 1 cm3 of isosulfan blue dye was injected submucosally via the colonoscope. The blue-stained lymphatics were visualized through the laparoscope and followed to the SLN, which was marked with a clip, and laparoscopic colectomy was completed in the routine fashion. All lymph nodes were examined by hematoxylin and eosin (H&E) staining; in addition each SLN was subjected to focused examination by multisectioning and immunohistochemical staining using cytokeratin antibody. In all 14 patients the primary neoplasm and an SLN were identified laparoscopically. An average of 13.5 total lymph nodes and 1.7 SLNs per patient were identified. The SLN correctly reflected the tumor status of the nodal basin in 93 per cent of the cases. In four cases with unexpected lymphatic drainage, the extent of mesenteric resection was altered. In two cases (14%), nodal involvement was micrometastatic, confined to an SLN, and identified only by immunohistochemical staining. Lymphatic mapping caused no complications and added only 10 to 15 minutes to the overall operative time. Comparison of results in this group with results for a matched group of 14 patients undergoing SLN mapping during open colon resection showed that the laparoscopic technique had similar rates of accuracy and success. These preliminary findings indicate that colonoscopic/laparoscopic SLN mapping during laparoscopic colon resection is a feasible and technically simple means of identifying the primary colorectal neoplasm and its SLN. Focused pathologic examination of this node can upstage CRC and thereby may improve selection of patients for adjuvant chemotherapy.