The incidence of BCL-6 gene rearrangement was studied in 39 Hong Kong Chinese patients with diffuse large B-cell lymphoma. The primary site of involvement was nodal in 18 cases and gastric in 21 cases. Clonal BCL-6 gene rearrangement was found in 17% of the patients with primary nodal and 48% with primary gastric lymphoma (p = 0.05). The clinical characteristics and treatment outcome of the 21 patients with primary gastric lymphoma were analyzed according to the BCL-6 status. Significantly more patients in the germline BCL-6 gene group had advanced stage (II, III and IV) of disease. Complete remission rate following primary therapy appeared to be higher for the positive rearrangement group (70% versus 36%), but it was not statistically significant. Those with a rearranged BCL-6 gene also appeared to have better survival at 5 years (58% versus 36%) but the difference was also not statistically significant. On the other hand, patients being classified as low risk according to the International Prognostic Index had significantly better survival at 5 years (89% versus 9%, p = 0.0001). We concluded that BCL-6 gene rearrangement was more commonly found in diffuse large B-cell lymphoma of primary gastric origin than its nodal counterpart and it may be playing a more important role in the pathogenesis of gastric large B-cell lymphoma. There was a trend that the BCL-6 gene rearrangement was associated with a more favorable outcome in patients with gastric large B-cell lymphoma but the difference was not statistically significant.