BACKGROUND Treatment of pediatric obstructive sleep apnea syndrome is surgical. The incidence of postoperative respiratory complications in this population is 5-25%. OBJECTIVE The aim of the authors was to present the preoperative evaluation and monitoring procedure elaborated in Heim Pál Children Hospital, Budapest. METHODS 142 patients were involved in the study. Patient history was obtained and physical examination was performed in all cases. Thereafter, polysomnography was carried out, the severity of the obstructive sleep apnea syndrome was determined, and the patients underwent tonsilloadenotomy. RESULTS 45 patients with mild, 50 patients with moderate and 47 patients with severe obstructive sleep apnea syndrome were diagnosed. There was no complication in patients with mild disease, while complications were observed in 6 patients in the moderate group and 24 patients in the severe group (desaturation, apnea, stridor, stop breathing) (p<0.000). In patients with severe obstructive sleep apnea syndrome, no significant difference was noted in preoperative apnoea-hypapnea index (p = 0.23) and in nadir oxygen saturation values (p = 0.73) between patients with and without complication. CONCLUSIONS Patients with severe obstructive sleep apnea syndrome should be treated in hospital where pediatric intensive care unit is available.