The aetiology of pelvic inflammatory disease (PID) has baffled researchers for years. One school of thought attributed its onset to organisms associated with sexually transmitted diseases, yet, such pathogens are found in only 50% of cases. Now, attention has turned to a new set of pathogens - anaerobic bacteria. These bacteria are associated with the onset of bacterial vaginosis, a condition that could be the missing link in PID aetiology. According to reports at the recent Anaerobe Society of the Americas' Congress on Anaerobic Bacteria and Anaerobic Infections held in California, US, this knowledge could help to form the basis of a new set of prevention strategies.