The usefulness of endoscopic ultrasonography (EUS) was assessed for diagnosing the depth of invasion in the gastric wall, the infiltration to the adjacent organs, and detecting regional lymph node involvement in primary gastric lymphoma. EUS was performed in 11 patients with primary gastric lymphoma who subsequently underwent gastrectomy with lymph node dissection, as well as chemotherapy in some cases. EUS findings showed a good correlation with the histopathology of the resected specimens. An accurate diagnosis of the depth of invasion into the gastric wall was made in 10 of 11 patients using the same T grade of the 1987 TNM system for gastric carcinoma. EUS also clearly visualized the reduction of depth of tumor invasion in two patients who underwent chemotherapy. Perigastric lymph node involvement could be detected accurately in nine of 11 patients. In conclusion, EUS is an excellent and sensitive diagnostic modality for the preoperative staging and follow-up of primary gastric lymphoma.