The mycoplasmas frequently isolated in genital tract, and potentially pathogenic, are M. hominis, U. urealyticum and M. genitalium. M. hominis and U. urealyticum are very frequent in the vaginal tract and they can be, according to circumstances, either commensal or pathogenic. M. hominis and/or U. urealyticum, have been considered as responsible for many types of genital infectious diseases (such as cervicitis, pelvis inflammatory disease), for infertility, obstetrical pathologies (premature delivery, premature rupture of membranes, chorio-amniotitis) and neonatal infections. Yet, most of the time, their actual responsibility has not been conclusively proven. Published data lack indisputable conclusions and in many fields, doubts still exist whether these mycoplasmas are pathogens or mere co-factors associated with genital infections. On the other hand, M. genitalium has been much less studied but it seems to be an unquestionable pathogen of genital tract; new studies will be necessary so that one has a better understanding of the pathologies it can induce.