OBJECTIVE The features of achondroplasia, the most common form of dwarfism, includes short cranial base and midface hypoplasia; both abnormalities increased the risk of upper airway obstruction during sleep. The aim of our study was to evaluate sleep and respiratory function of children with achondroplasia and to differentiate central from obstructive apnea. We also wanted to correlate apneic events with foramen magnum stenosis. METHODS Sixteen children with achondroplasia (mean age, 4.7 years) were studied by noctumal polysomnography and brain computed tomography or magnetic resonance imaging. A comparison of sleep and respiratory findings was made between the study group and 25 children with adenotonsillar hypertrophy. RESULTS The study revealed no significant difference between groups with respect to sleep architecture. We also found no relationship between apnea type and foramen magnum stenosis. Twelve children (75%) with achondroplasia had significant upper airway obstruction during sleep, with symptoms of continuous snoring and periods of brief obstructive apnea, hypopnea, or both. The mean apneahypopnea index (per hour of sleep) did not differ significantly between the two groups. However, the breathing rate during sleep was increased in children with achondroplasia. These findings indicate that the most important breathing disorder during sleep in children with achondroplasia is upper airway obstruction. CONCLUSIONS We conclude that polysomnography with detailed scoring of breathing abnormalities is a useful tool in evaluating sleep-disordered breathing in children with achondroplasia.