Combined regimen contraceptive steroids produce precocious endometrial secretion, followed by involution leading to a suppressed endometrium with small tubular glands and failure of spiral arterioles to develop; decidua-like stromal changes are dose related as is dilatation of venules. Thrombosis of the latter, perhaps estrogen mediated, leads to local tissue infarction and is the proximate cause of "breakthrough bleeding". Sequential regimen contraceptive steroids lead to retarded endometrial secretion, failure of spiral arterioles to develop, and a weak decidua-like stromal transformation. Contraceptive steroids occasionally produce polypoid lesions of the endocervix with atypical microglandular hyperplasia. There are conflicting reports about the effects of contraceptive steroids on the squamous epithelium of the exocervix, but they neither protect against cancer nor cause it in the usually accepted sense. Uterine leiomyomas may exhibit increased cellularity and bizarre, hyperchromatic nuclei or mutinucleation in women receiving contraceptive steroids. Both polyethylene and metal-containing intrauterine devices may initiate inflammatory responses in the endometrium varying from mild to severe, related to the time the device has been in contact with the mucosa. Salpingitis and ectopic pregnancy are increased in frequency in device users.