A large series of primary gastric lymphomas with long-term follow-up (average, 12.8 years) is reported. A number of factors known to affect nodal lymphoma were examined. Five- and ten-year survival rates were 57 and 46%, respectively. Statistically significant favorable prognostic variables were smaller tumor size (less than or equal to 7 cm), superficial mural invasion (submucosal only), and pathologic Stage I disease; these variables were intimately interrelated. A favorable influence on survival was discerned concerning histologic type and nodular histology, although still below statistical significance. No significant relation to survival was observed concerning clinical weight loss or palpable mass, vascular invasion, mode of therapy, or histologic subtypes of "histocytic" lymphoma. Of patients who succumbed to disease, 75% did so within two years (average, 1.8 years); however, later recurrence and death may occur. An argument for resection of localized disease is presented. Mitotic index and nuclear diameter were of diagnostic importance, and associated lesions such as pseudolymphomas are discussed in relation to pathogenesis. Histologic variation within tumors suggested visualization of clonal development in non-Hodgkin's lymphomas.