PURPOSE OF THE REVIEW: This review considers the roles of Chlamydia spp. and newly identified Chlamydia-like organisms in miscarriage, stillbirths and preterm labour in both animals and humans. RECENT FINDINGS: The cause of miscarriage, stillbirth and preterm labour often remains unexplained. Intracellular bacteria that grow either poorly or not at all on media used routinely to detect human pathogens could be the aetiological agents of these obstetrical conditions. There is growing evidence that Chlamydia trachomatis, Chlamydophila abortus, Chlamydophila psittaci and Chlamydophila pneumoniae infections may result in adverse pregnancy outcomes in humans and/or animals. Waddlia, a Chlamydia-like organism first isolated from an aborted bovine, has emerged as an agent of abortion in cattle. Recently, Waddlia was also implicated in human foetal death. Moreover, Parachlamydia acanthamoebae is also abortigenic in ruminants. Whether additional novel Chlamydia-like organisms, such as Protochlamydia amoebophila, Neochlamydia hartmanellae, Criblamydia sequanensis, Rhabdochlamydia crassificans and Simkania negevensis, are involved in foetal loss or premature delivery remains to be determined. SUMMARY: This review provides an update on the consequences of chlamydial infection during pregnancy and summarizes current evidence suggesting that some Chlamydia-related organisms are probably emerging obstetrical pathogens.