Oral cavity lymphoma (OCL) seems to occur more frequently in HIV-positive patients, but it is presently unknown whether HIV-related immune deficit plays a role in modifying the prevalence and the characteristics of these lymphomas. To clarify this issue, we compared OCL occurring in immunocompetent and HIV-positive patients. A comparison was made between cases of OCL occurring among 543 and 123 NHL consecutively diagnosed at a single center in immunocompetent and HIV-positive patients respectively. The prevalence of oral cavity involvement at diagnosis was significantly lower in the immunocompetent subgroup (HIV-negative: 1.66%; HIV-positive: 7.3%, P = 0.002). Extranodal T/NK nasal-nasal-type lymphoma (ET/NK-NL) was observed in 3 of 9 immunocompetent patients, whereas plasmablastic lymphoma (PBL) was observed in 3 of 9 HIV-positive patients. EBV expression correlated with HIV-positivity. Response to treatment was similar between the two subgroups, but the overall prognosis was significantly worse among HIV-positive patients. Median survival was 34 months in immunocompetent vs. 9 months in HIV-positive patients (P < 0.01). A higher frequency of oral cavity lymphoma was associated with HIV infection. ET/NK-NL and PBL seemed to be clinical entities characteristically related to immunocompetent and HIV-positive subgroups, respectively. Chemotherapy was feasible and effective in both subgroups, although a poor prognosis was associated with immunodeficiency.