Kaposi sarcoma (KS), a multifocal angioproliferative disorder, occurs most commonly in patients with AIDS, in whom it remains an important cause of morbidity and mortality. KS is often in the differential diagnosis in HIV- infected patients undergoing fine-needle aspiration (FNA). FNA diagnosis of KS is usually made by morphologic observation of scant tissue fragments composed of bland spindle cells and crush artifact. Human herpesvirus-8 (HHV- 8) has been identified by polymerase chain reaction (PCR) amplification of DNA samples isolated from various epidemiologic forms of KS. In an attempt to improve the accuracy of KS diagnosis by FNA, we analyzed for the presence of HHV-8 DNA in 13 spindle-cell lesions evaluated by FNA: KS, 8 cases; granulomatous inflammation due to Mycobacterium avium-intracellulare, 1; nodular fasciitis, 1; dermatofibrosarcoma protuberans, 1; dermatofibroma, 1; benign spindle-cell lesion of nerve sheath origin, 1; and 2 lesions with lymphoid hyperplasia. DNA isolated from archival Wright-Giemsa-stained glass slides was used for the PCR amplification of the HHV-8 DNA sequences. All of the cases diagnosed as KS and 1 of the lymphoid hyperplasia cases were PCR- positive for HHV-8 DNA, while all other cases of spindle-cell lesions were negative. The molecular demonstration of HHV-8 DNA may be a useful adjunct in the diagnosis of KS by FNA.