Urogenital mycoplasmas Ureaplasma urealyticum, Ureaplasma parvum and Mycoplasma hominis have long been considered commensals of human urogenital microflora. Several studies have recently clarified whether these bacteria could cause or be associated with various obstetric complications. Epidemiologic studies have found high prevalence of Ureaplasma spp. and M. hominis among otherwise healthy population. On the other hand, U. urealyticum, U. parvum and M. hominis have increasingly been linked to adverse pregnancy outcomes such as spontaneous pre-term labor, pre-term premature rupture of fetal membranes, miscarriage, stillbirth and low birth weight. However, no convincing causal relationship has been shown. Studies have shown that antibiotics resistance is on the rise and differs considerably by regions. Screening of asymptomatic patients for M. hominis, U. urealyticum and U. parvum is currently still not indicated.