The sexually transmissible pathogenic microorganisms, which are also capable of initiating pre- or perinatal infections, include Neisseria gonorrhoeae, Treponema pallidum, Chlamydia trachomatis serovars D through K, group B streptococci, urogenital mycoplasmas, herpes simplex viruses types I and II, cytomegalo-virus, hepatitis B virus, human immunodeficiency viruses, human papilomaviruses, Candida spp. and Trichomonas vaginalis. With special emphasis on paediatric and neonatological aspects, brief discussions of the following topics are presented: the epidemiology of these agents, the diseases they can induce in pregnancy, the mode of infection of and the diseases in the fetus and neonate, the preventive measures, the diagnosis and therapy.