Acute maxillary sinusitis is a common disorder affecting children. Untreated acute sinusitis can develop into chronic sinusitis, and complications, such as orbital cellulitis 0r abscess, can occur. Maxillary sinusitis of odontogenic origin is not a well-recognized condition and is frequently missed in children. As an odontogenic source of sinusitis, the dentigerous cyst is one of the most prevalent types of odontogenic cysts, and it is associated with the crown of an unerupted or developing tooth. This report concerns a nine-year—old boy who was diagnosed with maxillary sinusitis originating from a dentigerous cyst with supernumerary teeth. The boy visited our pediatric clinic presenting with rhinorrhea and nasal obstruction and was initially diagnosed with maxillary sinusitis only. With antibiotic treatment, his symptoms seemed to improve, but after 2 months, he came to our clinic with left facial swelling with persistent rhinorrhea and nasal obstruction. Radiographic examinations of the sinuses were performed, and he was diagnosed with maxillary sinusitis originating from a dentigerous cyst with supernumerary teeth. After a surgical procedure involving the removal of the dentigerous cyst with supernumerary teeth, the symptoms of sinusitis gradually diminished. There are only very few cases in the pediatric medical literature that remind us that odontogenic origin can cause maxillary sinusitis in children. Our patient can act as a reminder to general pediatricians to include dentigerous cysts in the differential diagnosis of maxillary sinusitis.