We evaluated the change of the cross sectional area and the volume of the nasal cavity and the nasopharynx after tonsillectomy and adenoidectomy. 31 cases received adenotonsillectomy from september 1993 to march 1994 were analized. We measured the area and the volume of the nasal cavity and the nasopharynx by the acoustic rhinometry preoperatively and postoperatively. We obtained the following acoustic rhinometric data. The areas of isthmus nasi were 0.44cm2 preoperatively and 0.46cm2 postoperatively(p=0.031). The areas of the anterior end of inferior turbinate were 0.53cm2 preoperatively and 0.65cm2 postoperatively(p=0.001). The nasal volume were 7.13cm3 preoperatively and 9.38cm3 postoperatively(p=0.001). The nasopharyngeal areas at the adenoid were 1.5cm2 preoperatively and 1.83cm2 postoperatively(p=0.029). Thies results indicated significant increase in the nasopharyngeal area at the site of the adenoid, the area of anterior end of inferior turbinate and the nasal volume after adenotonsillectomy.