Background: Paranasal sinusitis is frequently encountered in clinical practice. The application of imaging techniques has highlighted the high incidence of incidental sinus abnormalities. Additionally, the adverse impact of smoking on paranasal sinusitis has been verified; however, few studies have compared the characteristics of affected sinuses between non-smokers and smokers. This study aimed to assess the prevalence of paranasal sinusitis detected by magnetic resonance imaging (MRI) and determine its characteristics and affected sinuses in smokers. Methods: This cross-sectional study involved 4813 participants from two communities in Shanghai, China. Demographic data were recorded, and participants underwent a physical examination and head MRI. Logistic regression analysis was used to examine the relationship between smoking and paranasal sinusitis and the Cochran–Armitage test to analyze age-specific prevalence of paranasal sinusitis in smokers versus non-smokers. Results: Among the 4813 participants (2368 men, 2445 women; mean age, 53.0±10.1 years), the prevalence of paranasal sinusitis was 15.4 %, being higher in men (20.1 %) than in women (10.8 %; p<0.001). Paranasal sinusitis was significantly associated with smoking (adjusted OR=1.37, 95 % CI=1.10–1.70), and in smokers, it occurred most often in the maxillary sinus (19.1 %), followed by ethmoid (2.9 %), frontal (2.2 %), and sphenoid (1.8 %) sinuses. Conclusion: The prevalence of paranasal sinusitis was 15.4 % in Chinese adults aged 35–75 years. This gradually increased with age, reaching a peak at 55 years and stabilizing thereafter. In smokers, sinusitis occurred more often in the anterior nasal sinuses. (Clinical Trials. gov number: NCT00926172)