Diseases of the maxillary sinus and maxillary dentition frequently have overlapping symptoms and presentation. As a result, they may be misdiagnosed or failed to be diagnosed. We report a case of a 16-year-old girl with a two-day history of right facial swelling which was painful. She had rhinitis but denied any toothache. Her nasoendoscopic examination was normal but there was mild caries of her upper incisors with a right upper gum swelling. She was diagnosed with facial cellulitis secondary to apical periodontitis. Her symptoms resolved with drainage and systemic antibiotics. We wish to highlight the fact that dental infections may be present despite the absence of toothache and the importance of a detailed examination of the oral cavity and dentition in patients with suspected sinusitis to avoid a missed diagnosis.