The aim of the present study was to analyze in a series of 24 HIV-positive Hodgkin's disease (HD) patients the morphological and immunological features, the presence of rearrangements in the immunoglobulin heavy chain (IgH) gene, expression of the Epstein-Barr virus (EBV) latent membrane protein-1 (LMP-1), and the existence of deletions in the intracytoplasmic domain of the LMP-1 gene. The results obtained were compared with those from a parallel series of 56 patients with ordinary HD. Briefly, comparison of the two series showed a predominance of unfavorable histological subtypes in HIV-positive HD patients. The mixed cellularity subtype was more frequent in HIV-positive than in HIV-negative HD patients: the difference in percentage was statistically significant (p = 0.04). Neoplastic cell-rich cases were significantly more frequent (p = 0.40) in HIV patients (59%) than in ordinary HD patients (34%). In 25% of HIV-infected and in 14% of ordinary HD patients, the neoplastic cells were CD20+, a difference that was not statistically representative. Clonal IgH rearrangements were detected in 33% of HIV-infected patients and in 23% of ordinary HD patients, a nonsignificant difference. LMP-1 expression was detected in 100% of HIV-positive patients and in 57% of ordinary HD patients (p = 0.004). A 30-base-pair deletion in the carboxy-terminal domain of the LMP-1 gene was found in 16 of 18 HIV-infected patients (89%), whereas it was identified in only 8 of 25 ordinary HD patients (32%) (p = 0.008). In conclusion, HD in HIV-infected patients as compared with HD in HIV-negative individuals is associated with morphological features of aggressivity, with a higher frequency of neoplastic cells, and with constant LMP-1 expression. The fact that LMP-1 is expressed in all HIV-infected patients suggests that EBV plays an etiological role in the pathogenesis of HIV-associated HD. Furthermore, the presence of EBV strains carrying deletions near the 3' end of the LMP-1 gene in the majority of cases may be related with the morphological and clinical aggressivity of HD in immunocompromised patients.