To delineate the pitfalls and counter-measures in the endoscopic diagnosis of gastric malignant lymphoma (GML), reviewed were 32 cases of primary GML and 16 cases of systemic ML with gastric involvement (secondary GML). 1) Accurate diagnosis of GML had been made in only 13 cases of primary GML ; 18 cases had been diagnosed of gastric cancer (GC); the remaining one of benign ulcer (BU). Review of the endoscopic films, however, revealed more than two of the three findings characteristic, but not pathognomomic, of GML in 84 percent. This result indicates that possibility of GML must be kept in mind in the differential diagnosis of malignant lesions despite its rarity, because endoscopists tend to be predisposed with an impression of GC. 2) Follow-up examinations made in nine cases of primary GML revealed marked changes in endoscopic findings in three cases : healing of an ulcer lesion in one case, healing of an ulcer lesion on an unchanged tumor in another and enlargement of a tumor in the remaining one. The first case had been followed up for two years with an impression of BU. This result indicates that improvement of ulcer does not necessarily rule out GML because it can show "malignant cycle" just as GC. 3) Endoscopic biopsy performed in 30 cases of primary GML had led to accurate diagnosis in only 16 cases and erroneous diagnosis of GC in five and no malignancy in nine. Review of the cases revealed the importance of having suspicion of GML at first from endoscopic findings, because it can lead to an increase of the number of biopsy specimens, careful selection of biopsy sites, careful use of biopsy instruments to obtain good specimens and closer contact with pathologists. 4) Prospective studies on systemic ML revealed gastric involvement in 17 percent. Examinations of the GI tract, especially of the stomach is one of the important steps for staging of systemic ML and deciding therapeutic modalities. 5) It is extremely difficult to diffierentate primary GML and secondary GML from endoscopic findings alone, although there are a few findings characteristic of the latter.