A 28-year-old male patient with a history of cystic fibrosis (CF) was referred to the University of Connecticut School of Dental Medicine for an evaluation of a cystic lesion in the right maxilla using cone-beam computed tomography (CBCT). CF is an autosomal recessive disease characterized by an abnormal production of viscous mucus, affecting the mucociliary clearance. The CBCT scan revealed a large cystic lesion in the right maxilla extending from the right maxillary second molar to the midline in the region of the right central incisor with a significant buccal expansion. Further evaluation revealed complete opacification of the paranasal sinuses with medial bulging of the lateral maxillary sinus walls. The maxillary and sphenoid sinuses also appeared hypoplastic. The peculiar finding seen in this case was the presence of marked sclerosis and an increase in the thickness of the adjacent bony framework. This report aimed to describe the common sinonasal findings associated with CF and its underlying pathophysiology.