This paper addresses the problem of adverse pregnancy outcome in relation to periodontal disease. There is compelling evidence that a link exists between pre-term low birth weight (PLBW) and periodontitis. Although 25% to 50% of PLBW deliveries occur without any known aetiology, there is increasing evidence that infection may play a significant role in pre-term delivery. A model explaining the plausible relationship is proposed based upon the concept of infection leading to a cascade of inflammatory reactions associated with pre-term labour and periodontal disease. Current evidence has pointed to an interest in dental intervention studies to control periodontal disease as one of the potential strategies to reduce pre-term labour. This paper reviews the potential association between periodontal infection and adverse pregnancy outcomes.