BACKGROUND: This study was undertaken to analyze the necessity of deflating cuff volume to maintain intracuff pressure of the laryngeal mask airway (LMA) under 44 mmHg in general anesthesia with propofol and N2O. METHODS: In 168 surgical patients, LMA was inserted (male: #5, female: #4) and the cuff was sealed with air under positive pressure ventilation with 7-8 ml/kg of tidal volume. After measuring the initial intracuff pressure (P0), the intracuff volume (V0) of LMA and peak inspiratory pressure (PIP0), N2O (50%) was administered, and the time for the intracuff pressure to reach a pressure of 44 mmHg (T44), the intracuff volume for the intracuff pressure to reduce to P0 (Vdef), the N2O inhaled time and the number of patients who needed deflation were recorded. RESULTS: P0, V0, PIP0 were 24+/-7.5 mmHg, 17+/-2.8 ml, 13+/-3.8 cmH2O in males and 27+/-8.2 mmHg, 14+/-2.3 ml, 13+/-4.0 cm H2O in females, respectively. The number of patients who needed cuff deflation after inhaling N2O was 17 (18.5%) in males and 36 (47.4%) in females. T44 and Vdef were 27+/-16 min, 1.9+/-0.8 ml in males and 26+/-21 min and 1.3+/-0.6 ml in females, respectively. The necessity for LMA cuff deflation was related to P0, V0, and the N2O inhaled time in males and to P0 and the N2O inhaled time in females (P <0.05). CONCLUSIONS: In anesthesia with N2O, if the initial intracuff pressure of LMA is high and the duration of anesthesia prolonged, careful monitoring of the intracuff pressure is necessary.