OBJECTIVE To determine whether bispectral analysis (BIS) changes during nitrous oxide (N(2)O) sedation in anxious children undergoing extraction of primary teeth. METHODS In this prospective study 45, ASA physical status I children, aged between 7 to 12 years and scheduled for primary teeth extraction under N(2)O/O(2) sedation are included. At baseline (T0) and during the sedation procedure (T1-6); BIS levels, Ramsay Sedation Scores (RSS), oxygen saturation (Sp0(2)), and heart rate (HR) were recorded at one-minute intervals. Forty percent N(2)O in O(2) was given by a nasal hood, and N(2)O concentration was enhanced to 60% in a two-minute period. Paired measurements of BIS levels with Observer's Assessment of Alertness and Sedation (OAA/S) scores were obtained during sedation procedure. RESULTS Since 5 patients refused application of the nasal hood, a total 40 of the original 45 subjects completed the study. Mean age and weight of the children were 9.5 +/- 1.4 years and 23.7 +/- 9.7 kg, respectively. Nitrous oxide inhalation produced no changes in BIS levels despite a sedation level in OAA/S scores were observed at 40-60% N(2)O concentrations. CONCLUSIONS BIS values do not change during N(2)O/O(2) sedation and the BIS monitor is not appropriate to evaluate the depth of sedation provided by N(2)O/O(2) during primary teeth extraction in children.