Our objective was to evaluate the usefulness of acoustic pharyngometry and rhinometry in assessing obstructive sleep apnea (OSA) syndrome in children.Patients who were hospitalized for polysomnography underwent acoustic pharyngometry and rhinometry in sitting and supine positions to measure anatomical (pharyngeal and nasopharyngeal) volumes and collapsibility characteristics (reduction of pharyngeal volume, estimated pharyngeal compliance, and reduction of nasopharyngeal volume).In this study, we prospectively enrolled 103 children (median age, 10.4 years; 47 girls). Measures obtained from rhinometry correlated with height and were further height-normalized whereas measures obtained from pharyngometry did not correlate with height. Sleep apnea was ruled out in 51 subjects, while 52 children fulfilled OSA criteria (35 with obstructive apnea-hypopnea index ≥ 2 and < 5.h [mild] and 17 with an index ≥ 5). The three groups differed on the z-score of BMI, the reduction of pharyngeal volume when supine, the estimated pharyngeal compliance and the supine normalized nasopharyngeal volume. These four factors linearly correlated with the apnea index even though children without OSA and mild OSA were found to be similar overall. A multivariate analysis with apnea index as the dependent variable and BMI z-score, neck circumference, mean pharyngeal area in supine position, estimated pharyngeal compliance and normalized nasopharyngeal volume as independent variables, showed that only BMI z-score and estimated compliance remained independent predictors of obstructive apnea (r value = 0.25, p < 0.0001).An increase in pharyngeal compliance is an independent risk factor of OSA syndrome in children; it can be measured using acoustic pharyngometry while awake.