The presence of Ureaplasma urealyticum was evaluated on 1912 vaginal and urethral swabs from HIV-1 seronegative (HIV-) inpatients (210) and outpatients (503) suffering from acute urethritis or vaginitis; asymptomatic HIV- outpatients (201); and asymptomatic HIV-1 seropositive (HIV+) inpatients (120). The study reported an increased frequency of Ureaplasma urealyticum isolates in asymptomatic HIV+ compared to asymptomatic HIV- subjects. As expected, the frequency of Ureaplasma urealyticum isolates increased in symptomatic HIV- subjects. Strains of Ureaplasma urealyticum resistant to ciprofloxacin, tetracycline and minocycline were more frequently isolated in HIV+ (34.1%) than HIV- (3.8%) subjects; on the other hand, only 1 out of 704 (0.1%) strains isolated from outpatients was resistant to ciprofloxacin. We found no association in HIV+ patients between Ureaplasma urealyticum infection and CD4 count or HIV-1 p24 antigenemia.