This paper reviews primary gastrointestinal non-Hodgkin's lymphoma (GI-NHL). Every aspect of the topic is discussed though special attention is paid to histopathology and instrumental diagnosis as essential factors to stage the lymphoma and to determine an adequate therapy. Data from the most important works on the subject together with the results of our recent study of 40 primary GI-NHL are reported. Diverse findings by various authors are intentionally compared in a manner to present the work to the reader in the most critical way while trying to give an objective explanation of the different results on the basis of our own experience.