Clinicopathologic information of gastrointestinal (GI) lymphoma in Southeast 
Asia is lacking. A retrospective analysis of 120 cases of GI lymphoma in 
Thailand diagnosed at Siriraj Hospital based on WHO classification was 
performed. All were non-Hodgkin lymphoma (NHL). The peak age was in the sixth 
and seventh decades; a slight male preponderance was observed. Sites of 
involvement included stomach (49.2%), intestine (46.7%), and multiple sites 
(4.2%). There were 104 cases of primary GI lymphoma (86.7%) and 16 cases of 
secondary GI lymphoma (13.3%). Presenting GI symptoms were more common in the 
former; while superficial lymphadenopathy and fever were more common in the 
latter. Mass lesions were observed in both groups (72.1% vs 56.3%). Localized 
and advanced diseases were found in 68.3% and 31.7% of primary GI lymphomas, 
respectively. The most common type of lymphoma in both groups was diffuse large 
B-cell lymphoma. Lymphoepithelial lesions (LEL) were not significantly different 
between the two groups (58.2% vs 42.9%), but Helicobacterpylori infection was 
significantly associated with primary gastric lymphoma (p < 0.0001). The 
treatment of choice for localized primary GI lymphoma is controversial. Complete 
surgical resection may increase the chance of complete remission, but mortality 
and relapse rates might be higher than those observed with combination 
chemotherapy alone. GI lymphomas in Thailand are mostly primary B-cell NHL. LEL 
is not indicative of primary GI lymphoma, but H. pylori infection is closely 
associated with primary gastric lymphoma. A prospective study to determine the 
treatment of choice for localized GI lymphoma is needed.