A six-year-old healthy female with cystic fibrosis (CF) and pancreatic sufficiency presented with cough, weight loss, and lung function decline. Further history suggested obstructive sleep apnea, and nocturnal polysomnography (NPSG) confirmed this. Adenotonsillectomy resulted in resolution of clinical symptoms with return of normal lung function. This case establishes that obstructive sleep apnea syndrome (OSAS) may be a potential cause of lower airway inflammation and resulting weight loss in the young CF population.