Background There are few reports on a dual dye and isotope approach using laparoscopy in gastric cancer sentinel node mapping. The aim of this study is to evaluate the feasibility of laparoscopic sentinel basin dissection for gastric cancer using simultaneous indocyanine green (ICG) and 99m Tc-antimony sulfur colloid (ASC) injections. Methods Sixty-eight patients were enrolled who had been diagnosed with cT1–T2 and cN0 stage gastric cancers. They underwent laparoscopic sentinel basin dissection between June 2005 and May 2008. ICG and 99m Tc-tin colloid (separate injections in the first phase, n  = 16) or ICG and 99m Tc-ASC (simultaneous injections in the second phase, n  = 52) were injected into the submucosa endoscopically. After performing the sentinel basin dissection, laparoscopy-assisted gastrectomy with curative lymphadenectomy was done. Green-stained or radioactive sentinel nodes (SNs) were analyzed by hematoxylin and eosin staining and by immunohistochemistry for cytokeratin. Results SNs were identified in 62 of the 68 patients (91.2%; mean 3.3 per patient). Eighteen patients had lymph node metastases. The sensitivity and specificity were, respectively, 72.2 and 100% using the dye method and 83.3 and 100% by the isotope method. However, the dual dye/isotope procedure improved both sensitivity and specificity to 100%. Patients receiving this protocol had significantly more SNs than those receiving separate ICG and 99m Tc-tin colloid injections (3.3 vs. 1.9, P  = 0.008). Conclusion Simultaneous ICG and 99m Tc-ASC-guided laparoscopic sentinel basin dissection is an effective tool for gastric cancer SN mapping, giving a high detection rate and excellent sensitivity.