The genital mycoplasmas have been implicated in a number of adverse outcomes of pregnancy. Spontaneous preterm labour and preterm birth is an important contributor to perinatal mortality and morbidity. If Mycoplasma hominis plays an integral part in this problem, it is likely to contribute through its involvement with bacterial vaginosis. Ureaplasmas induce cytokines and inflammation, making a casual association compelling. The role of Mycoplasma genitalium and Mycoplasma fermentans is less clear, but M. genitalium is potentially pathogenic and should be treated if detected. There is considerable evidence for the role of M. hominis in post-partum and post-abortal sepsis, and for ureaplasmas causing chronic lung disease or death in very low birthweight infants. The role of the genital mycoplasmas in adverse outcomes of pregnancy is complicated by the presence or absence of bacterial vaginosis, and this association requires further research.