Copper-containing intrauterine devices (IUDs) for contraception are increasingly used within recent years. IUDs in situ provoke a non-specific inflammatory cell reaction, particularly at the glandular epithelium of the endometrium. The cellular changes include swelling of the cytoplasm and of the nuclei, the latter showing chromatin clumping, prominent nuclei and a pseudoeosinophilic reaction. Cytoplasmic changes exhibit vacuolation, incorporation of leukocytes and plasmolysis varying in degree. The local inflammation also accounts for the side effects associated with the device, such as uterine bleeding and endometritis. Cytomorphologically, the differentiation between cellular inflammation through IUDs and inflammatory metaplasia is difficult, particularly if the investigator has no information about the presence of an IUD. Intrauterine application of proteinase inhibitors can be helpful in differential diagnosis of such IUD-mediated cellular changes.