The clinicopathological features of human immunodeficiency virus (HIV)-associated lymphoma were investigated in a retrospective study of 85 adult patients in eastern Denmark diagnosed during the period 1990-1996. The possible pathogenetic role of Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8) in these tumours was also studied. Seventy patients (82%) presented with extranodal disease and 26 (31%) had CNS involvement at diagnosis. Diffuse large cell B-cell lymphoma was the most frequent histological subtype, comprising 65 of 79 cases available for microscopic re-evaluation (82%) and including 20 of 23 evaluable patients with CNS lymphoma (87%). EBV RNA was demonstrated by in situ hybridization in 51 of 65 evaluable tumours (79%) and in 14 of 16 cases (88%) with CNS-lymphoma. Three cases showed a T-cell phenotype. The presence of HHV-8 DNA was analysed by PCR in 32 cases. A strong band consistent with tumour cell infection was detected in only one case, weaker bands being seen in 4 cases. None of these patients had primary effusion lymphomas. In conclusion, Danish AIDS-related lymphomas are of predominantly high-grade B-cell type with extranodal localization and atypical presentation. Our results provide further evidence that EBV plays a major role in the pathogenesis of large cell AIDS-related lymphoma, whereas HHV-8 does not appear to contribute significantly to the development of solid lymphomas in this group of patients.