PURPOSE: In vitro sonography of lymph nodes was performed to ascertain the differential point between benignancy and malignancy. MATERIALS AND METHODS: Ninty-one lymph nodes were obtained at gastric cancer surgery and pathologically proved as benignancy in 68 and malignancy in 23 cases. Sohographic and pathologic correlation of resected ninty one lymph nodes was done in terms of size, the ratio of longest diameter versus shortest diameter, central hyperechogenicity, and peripheral cortical echo. RESULTS: Sonographic findings of benign lymph node were small size, oval shape(85%), narrow central high echogenicity(44%), and symmetric cortical thickening(41%). Sonographic findings of malignant lymph node were large size, round contour(39%), loss of central high echogenicity(82%), and diffuse increase of cortical thickness(82%). CONCLUSION: The most reliable sonographic criterion for differentiation of benignancy from malignancy was size of a lymphnode.