Lymphoma of the stomach may exist as a primary lesion or as a manifestation of generalized or systemic lymphoma. The primary lesions constitute approximately 3 per cent of all malignant lesions of the stomach and outnumber all other types of non-epithelial malignant lesions. The cause is not known. Gross characteristics often resemble carcinoma, and like carcinoma, the primary lesion may affect other structures by direct extension, may seed to peritoneal surfaces, may metastasize to lymph nodes near or far, and may be borne by the blood to liver, lung or bone. Diagnosis begins with clinical suspicion by the physician, is supported by the results of roentogenographic and gastroscopic studies, and is finally established by a positive study of biopsy specimens obtained with or without laparotomy. Improvements in both gastroscopic instruments and their use promise to increase greatly the accuracy of preoperative diagnosis. Pseudolymphoma of the stomach, a rare type of inflammatory lesion, may, on occasion, offer a difficult differential diagnosis from that of lymphoma. The clinical approach to the lesion, whether the diagnosis is histologically proved or not, is the same as for suspected carcinoma. A laparotomy is usually necessary to determine the possibility of surgical cure, unless distant spread or systemic involvement can be established by other means, such as a distant lymph node containing the disease or a positive needle biopsy of the liver. When a cure seems possible, resection is favored by most surgeons, even though it entails total gastrectomy or multiple organ resection. Opinion is divided as to whether or not a curative resection should be followed routinely by irradiation, although irradiation is generally favored by palliation of lesions not amenable to resection. Transgastroscopic biopsy and gastroscopic follow-up study may permit radiation to be tested as the only form of treatment of favorable lesions. At the present time, chemotherapy should be reserved for lesions not controlled by operation or irradiation. Stage for stage, the outlook for lymphoma of the stomach is about twice as favorable as that for carcinoma. No generally accepted classification of lymphoma exists as yet. Correlations between prognosis and microscopic characteristics are not close, except for the generally favorable outlook for lymphocytic lymphoma.