The clinicopathologic features of 45 human immunodeficiency virus (HIV)-infected patients (mainly intravenous drug users [IVDU]) with lymphoid neoplasias seen from September 1984 through July 1990 at an Italian cancer center are reviewed. Thirty-five had systemic non-Hodgkin's lymphoma (NHL), and ten had Hodgkin's disease (HD). Histologically, 27 NHL cases were intermediate grade (five cases) or high grade (22 cases, 14 of the small noncleaved cell type), according to the Working Formulation. Eight NHL cases, including four anaplastic large cell (ALC) BerH2 (CD30)-positive lymphomas, were in the miscellaneous group. Immunohistologic and/or gene rearrangement analysis showed the B-cell origin of 20 of the 24 NHL cases studied. At presentation, 71% of NHL patients had advanced stages (Stage III or IV), and 85% had extranodal disease (predominantly gastrointestinal tract and marrow). Of the 23 patients evaluable for treatment, only seven had a complete clinical response after lymphoma therapy; the median survival of 34 evaluable patients was 22 months after the diagnosis of NHL. Fifteen patients died; most deaths were attributable to progressive lymphoma and opportunistic infections. As with NHL, advanced disease, extranodal involvement, aggressive histologic findings, and poor response to therapy were also observed in patients with HD. This study shows that lymphoid neoplasias occurring in Italian IVDU with HIV infection and those previously reported in North American homosexual men with HIV infection share similar clinicopathologic features. However, some features such as the absence of history of Kaposi's sarcoma at diagnosis, the lack of detection of primary brain and rectal NHL, and the occurrence of B-cell ALC BerH2 (CD30)-positive NHL were observed uniquely in this series of patients.