Acute anterior uveitis (AAU) may be associated with systemic infectious or inflammatory disease. We examined 92 patients with the first attack of acute anterior uveitis; all patients were free of any extraocular symptoms. A thorough clinical examination did not reveal any systemic underlying disease. In the course of microbiological examination, however, a high incidence of asymptomatic infection of the urethra and/or cervix with ureaplasma urealyticum, chlamydia trachomatis and mycoplasma hominis was found. Infections with ureaplasma were significantly more frequent in patients with AAU when compared with a sex- and age-matched control group. There was no statistically valid association of these infections with the HLA-B27 phenotype in the patients. The higher rate of urogenital infections in patients with AAU may reflect a higher rate of sexual promiscuity. Transmission of infectious agents seems to be one possible factor in the pathogenesis of AAU.