Bacterial vaginosis (BV) is the most common vaginal infection worldwide. It has been linked to serious public health consequences including preterm birth, postoperative infections, and the acquisition and transmission of sexually transmitted diseases including HIV. The etiology of BV remains unknown. In this article, controversies about sexual transmission, microbial pathogens, and heterogeneity of BV as a disease entity are discussed. © Current Medicine Group, LLC 2009.