The classic laryngeal mask airway is one of the keystones of modern anaesthetic practice. It achieves a reliable airway with a low incidence of major complications and pharynges-laryngeal morbidity. The manufactures of laryngeal mask airway recommend the proper size selection by actual body weight. It was recommended a size 3 for 30-70kg, a size 4 for 70-90 kg, and size 5 for > 90 kg. Obesity increases the fat tissue around an upper airway and decreases the pharyngeal cross sectional area. Also it was reported that pharyngeal area was reduced according to the increasing of BMI. Therefore, the aim of this study is to determine which of actual body weight or ideal body weight is proper on the size selection of laryngeal mask airway.

Inclusion Criteria:

• age 20~70
• body mass index > 25 kg/m2
• patient who needs surgery with laryngeal mask airway

Exclusion Criteria:

• difficult airway
• upper airway infection or disease of airway
• history of gastroesophageal reflux
• history of head and neck surgery