Primary non-Hodgkin's lymphoma of the stomach represents a minority of 1-7% of all gastric malignancies. Symptoms are non-specific. At endoscopy three main patterns can be recognized: ulceration, diffuse infiltration, or a polypoid mass. Endoscopic biopsy results may be false-negative (up to 8%) owing to submucosal localization. The new technique of endoscopic ultrasonography is accurate in measuring depth of infiltration and regional lymph nodes. Preoperative diagnosis altered the indication for surgery. Without resection an excellent local tumour control (stage I, 85%, and stage II, 69%) can be achieved, leading to a fair prognosis: 5-year relapse free survival in stage I, 83%, and in stage II, 58%. Intra-abdominal recurrences were scarce (2%), and severe complications such as perforation and life-threatening haemorrhage were seldom present (4%). Thus, resection is not necessary, but early recognition is highly significant. Favourable results can be achieved by irradiation or chemotherapy with irradiation.