Introduction: Periodontitis and obesity are among the most common chronic disorders affecting the world's populations, and recent reviews suggest a potential link between overweight/obesity and periodontitis. However, due to the scarcity of prospective evidence, previous reviews were primarily based on cross-sectional studies, with only few longitudinal or intervention studies included. The objective was to examine the time-dependent association between obesity and periodontitis and how weight-changes may affect the development of periodontitis in the general population. Therefore, longitudinal and experimental studies that assessed the association between overweight, obesity, weight gain, waist circumference and periodontitis were reviewed Method: Intervention and longitudinal studies with overweight or obesity as their exposure and periodontitis as their outcome were searched through the platforms Pubmed/Medline and Web of Knowledge. Results: Eight longitudinal and five intervention studies were included. Two of the longitudinal studies found a direct association between degree of overweight at baseline and subsequent risk of developing periodontitis, and further three studies found a direct association between obesity and development of periodontitis among adults. Two intervention studies on the influence of obesity on periodontal treatment effects found that the response to non-surgical periodontal treatment was better among lean than obese patients, the remaining three studies did not report treatment differences between obese and lean. Among the eight longitudinal studies, one study adjusted for CRP and biological markers of inflammation such as CRP, IL-6 and TNFα and inflammation markers were analyzed separately in three of the five intervention studies. Conclusion: This systematic review suggests that overweight, obesity, weight gain and increased waist circumference may be risk factors for development or worsening with regard to periodontal measures.