Endoscopic ultrasonography (EUS) and endoscopy were prospectively performed and compared to the histopathologic findings of the resection specimens in 24 patients with primary gastric lymphoma (PGL). On EUS, three types of PGL could be differentiated, a superficial type (n = 10), an infiltrating type (n = 12) and a tumorous type (n = 2). In the correct assessment of surface extension of the tumors, endoscopy and EUS agreed in 37.5% of cases and EUS showed more extensive disease than endoscopy in 58% of cases. However, in comparison to the resection specimens, EUS still underestimated the tumor surface extension in 37.5% of cases; this was mainly in low grade malignant PGL. The depth of tumor infiltration was correctly determined on EUS compared to the resection specimens in 91.5% of cases. Sensitivity, specificity and accuracy of diagnosing lymph node metastases were 100%, 80% and 83%, respectively. We conclude that EUS is a useful pre-therapeutic staging tool for primary gastric lymphoma but there remain some problems in determining the longitudinal and circular tumor spread in order to accurately guide the extent of gastric resection.