We studied the prognostic significance of lymph vessel involvement in the gastric wall in 226 patients with advanced gastric cancer. There was no close correlation between the gross morphology of the cancer and the incidence of lymph vessel invasion. However, the more severe the degree of lymph vessel involvement, the higher was the incidence of lymph node metastasis. Severe lymph vessel invasion was found most frequently in poorly differentiated adenocarcinoma of the medullary type. Among patients with scirrhous carcinoma there were some in whom lymph vessel involvement was overlooked on routine histologic examination. Because the depth of lymph vessel invasion of the gastric wall was significantly related to the clinical course, we consider this to be of supplementary predictive value.