Oral hairy leukoplakia (HL) was observed in 25.4% of 373 HIV-seropositive patients (n = 95). 87 were men of an average age of 37.1 yr, 8 were women (30.3 yr). 71.6% of the patients were male homosexuals. At initial diagnosis of HL the majority of cases was classified as CDC IVc1 (45.3%) and CDC II (22.1%). Average CD4/CD8 ratio (n = 19) was 0.24 with a range of 0.04-1.0. Thirty biopsies of HL revealed some of the histologic features thought to be characteristic. In only 20 of 30 biopsies EB-virus-specific-capsid antigen was detected. The problems of clinical and histological diagnosis of HL are discussed. Further strict criteria are necessary in order to define HL more distinctly.