The aim of this study was to analyze the oral etiology of patients with odontogenic sinusitis (ODS) and to compare the differences in demographic data, clinical symptoms, extent of sinus involvement, bone penetration of the maxillary sinus floor (MSF) between different etiologies. A retrospective investigation was conducted on 103 patients with ODS recruited from Beijing TongRen Hospital. All enrolled patients underwent sinus CT, nasal endoscopy, and oral examination. A comparison of the patients' clinical symptoms, the extent of involvement of the sinuses, and bone resorption of the MSF according to odontogenic etiologies was conducted. Follow-up was based on symptoms and clinical examination. The most common odontogenic etiologies were endo-periodontal lesions (EPLs, 49.5%), apical periodontitis (AP, 32.0%), and periodontitis (PE, 8.7%). There were statistically significant differences in age (p = 0.002), sex (p = 0.036), inflammation involving the ethmoid sinus (p = 0.037), and bone penetration of the MSF (p < 0.001) between the AP, EPL, and PE groups. There were no significant differences in sinusitis symptoms (p > 0.005) among patients with different odontogenic etiologies. In conclusion, EPL is a neglected oral etiology with a destructive effect on the bone of the MSF, which deserves more attention in diagnosis and treatment.