The objective of this study was to assess the prevalence of Ureaplasma urealyticum and Mycoplasma hominis infections and to investigate associations between their presence in the lower female genital tract and lifestyle characteristics. The study was performed on a population of 3115 women, comparing the demographic and behavioural characteristics of 872 women with U. urealyticum infection and 142 women with M. hominis with uninfected women, using univariate and multiple logistic regression analysis. The prevalence of infection with U. urealyticum was 28% and M. hominis was 4·6%. In multivariate logistic regression analysis, intrauterine device, number of sexual partners and age (<35 years) were significantly associated with U. urealyticum while previous induced abortion, condom use and young age at first intercourse (<16 years) were associated with M. hominis infection. U. urealyticum infection presents the same demographic and behavioural characteristics of a sexually transmitted disease. The unprotective role of condom use suggests a non-sexual mode of transmission of M. hominis infection.