Objectives: Odontogenic sinusitis usually affects the maxillary sinus but may extend to the anterior ethmoid sinuses. The purpose of this study is to determine the percentage of odontogenic maxillary sinusitis extended to the anterior ethmoid sinuses and determine also the surgical resolution differences between odontogenic maxillary sinusitis and odontogenic maxillary associated to anterior ethmoidal sinusitis. Study Design: This is a retrospective cohort study performed on 55 patients diagnosed of odontogenic sinusitis and treated surgically by functional endoscopic sinus surgery. Results: This study showed that 52.7% of odontogenic maxillary sinusitis spreads to anterior ethmoid, causing added anterior ethmoid sinusitis. We found that 92.3% of the odontogenic maxillary sinusitis (who underwent middle meatal antrostomy) and 96.5% of the odontogenic maxillary sinusitis extended to the anterior ethmoid (treated with middle meatal antrostomy and anterior ethmoidectomy) were cured. Conclusions: Ethmoid involvement is frequent in maxillary odontogenic sinusitis. The ethmoid involvement does not worsen the results of “functional endoscopic sinus surgery” applied to the odontogenic sinusitis. Key words:Odontogenic maxillary sinusitis, ethmoiditis, functional endoscopic sinus surgery.