Background: Mucosal thickening and mucosal cysts of the maxillary sinus are commonly observed among asymptomatic subjects. The role of dental diseases on these abnormalities was unclear. The aim of this study is to determine the relationship between dental diseases and mucosal thickening/ mucosal cysts of the maxillary sinus. Methods: The computed tomographic (CT) images of 250 consecutive subjects who underwent CT scans for dental treatment purposes were studied. Dental findings including periodontal bone loss, periapical lesions, and root canal fillings were assessed. The presence of mucosal thickening and mucosal cyst of the maxillary sinus was recorded. Logistic regression analysis was used to determine the influence of dental findings on these sinus mucosal abnormalities. Results: The prevalence of mucosal thickening was 42% and of mucosal cysts was16.4% of subjects, both being more frequent in males than in females. Periodontal bone loss was significantly associated with mucosal thickening whereas periapical lesions and root canal fillings were not. Presence of severe periodontal bone loss increased risk of mucosal thickening by 3 folds (OR=3.02, P<0.001). There was no association between dental findings and mucosal cysts. Conclusions: Severe periodontal bone loss was significantly associated with mucosal thickening of the maxillary sinus. Mucosal cysts were not associated with any dental findings.