A cross-sectional study was conducted among pregnant women in Côte d'Ivoire to assess the prevalence and the factors associated with mycoplasma colonization. A positive culture was found in 400 of 551 women (73%); Ureaplasma urealyticum was identified in 22%, Mycoplasma hominis in 20% and both microorganisms in 31%. Mycoplasma colonization was not associated with genital symptoms or signs. Young age, low educational level, antimicrobial chemotherapy before consultation and presence of bacterial vaginosis were factors independently associated with M. hominis colonization. Among women colonized with M. hominis, HIV seroprevalence was 21% in women with high amounts of M. hominis (> or = 10(4) colour-changing units per ml) versus 7% in women with lower amounts (P=0.01). U. urealyticum was found more often in unmarried women and when pregnancy was less than 20 weeks. Mycoplasma colonization is frequent among pregnant women in Abidjan, but their pathogenicity requires further study.