We analyzed a cohort of 400 patients referred from the otorhinolaryngology department (40.05 %), primary care (PC) (36.52 %), and the pediatric pulmonary unit (17.63 %). The children were referred for clinical suspicion of apneas in 191 (47.87 %), snoring and apneas in 101 (25 %), and snoring in 87 (21.80 %). Adenotonsillar hypertrophy was found in 211 patients (52.75 %), tonsillar hypertrophy in 87 (21.75 %), and adenoid hypertrophy in 73 (18.25 %). All patients underwent respiratory polygraphy (RP) during sleep. Obstructive sleep apnea-hypopnea syndrome (OSAHS) was diagnosed in 298 patients (74.5 %). OSAHS was mild in 96 patients (24 %), moderate in 148 (37 %), and severe in 54 (13.5 %). The results of RP expressed in means plus standard deviation were as follows: number of apneas 21.38 (24.47), number of hypopneas 19.81 (20.74), apnea-hypopnea index per hour (AHI/h) 5.29 (7.10), mean oxygen saturation 94.60 (11.80), minimal saturation 83.14 (13.45), number of snores 98.27 (254.55), and snoring index per hour 5.68 (6.5). Significant differences were found between oxygen saturation and AHI/h per hour. No differences were found among age, mean oxygen saturation, area of residence, reason for consulting, and AHI/h. Adenotonsillectomy was performed in 289 patients (72.25 %) of the initial cohort. In conclusion, OSAHS in childhood is frequent. RP during sleep aids diagnosis. The main cause of OSAHS in children is adenotonsillar hypertrophy.