Maternal infections are known to play a major role in perinatal morbidity and mortality. Ureaplasma urealyticum and Mycoplasma hominis are sexually transmissible microorganisms associated with a number of pathologic conditions in the pregnant woman including chorioamnionitis and postpartum fever. They are rapidly gaining recognition as significant causes of perinatal infection, especially in infants born prematurely. This review summarizes current knowledge regarding the epidemiology, pathology, disease spectrum, and clinical manifestations of mycoplasmal and ureaplasmal perinatal infections and presents guidelines for proper diagnosis and treatment.