In mucopolysaccharidoses, upper airway obstruction has multiple causative factors and progressive respiratory disease may severely affect morbidity and mortality. In a cross-sectional study over 2 years we evaluated upper airway obstructive disease through overnight polysomnography, upper airway computed tomography and nasal endoscopy in 5 children and 6 adults with mucopolysaccharidoses of various types. Measurements of apnoea and apnoea-hypopnoea index, arousal index, and sleep efficiency were obtained through polysomnography. Retropalatal and retroglossal spaces were calculated through computed tomography, and the degree of adenoid hypertrophy was assessed through endoscopy. Apnoea index and apnoea-hypopnoea index were significantly higher in children than in adults with mucopolysaccharidoses (p = 0.03 and p = 0.03, respectively). Compared to healthy controls, retropalatal and retroglossal spaces were significantly smaller in children (p = 0.03 and p = 0.004, respectively) or adults with mucopolysaccharidoses (p = 0.004 and p = 0.004, respectively). All subjects had adenoid hypertrophy causing first-degree (36%) or second-degree (64%) obstruction at endoscopy. Overnight polysomnography, upper airway computed tomography and nasal endoscopy are useful tools for diagnosing obstructive sleep apnoea syndrome in mucopolysaccharidoses, and identifying the site and severity of airway obstruction.