AIM To study the relationship between the presence of apical periodontitis in root-filled teeth and marginal bone loss (MBL) in individual subjects from a general population. MATERIALS AND METHODS The study was conducted on a sample of 1,152 dentate individuals (participants in an epdemiological investigation) who were subjected to clinical and radiographic investigations. The presence of root fillings and apical periodontitis were registered. MBL was measured mesially and distally at all roots. The MBL index of the subject was defined as the mean MBL value at all measurable points in the same individual. Multiple regression analysis was adopted to calculate the influence of the presence of apical periodontitis and potential confounders on the dependent variable, MBL index. RESULTS There was a significant correlation between MBL and the percentage of root-filled teeth and the percentage of root-filled teeth with apical periodontitis. The results of the multiple regression analysis showed that the relative frequency of root-filled teeth with apical periodontitis was significantly higher in subjects with more MBL, irrespective of age, number of remaining teeth, relative frequency of root-filled teeth and smoking habits. CONCLUSIONS A significant association between the presence of apical and marginal periodontitis in individual subjects was found. The mechanisms behind the associations between these diseases are unknown and this cross-sectional observational study did not permit distinction between cause and effect. It is hoped that future cohort studies may provide more knowledge about the biological actions behind the relationship between apical and marginal disease.