Objective: Purpose of this study was to find out the effect of positional change and inhalant anesthesia on acoustic reflectometry (AR) parameters (reflectivity and curve angle). Method: AR parameters were measured on 58 ears with otitis media in sitting position before anesthesia and in supine position under inhalant anesthesia, subsequently. Results: Under anesthesia, ears with effusion disclosed more changes in reflectivity (Chi-squared analysis, χ2-test; P<0.05) and curve angle (P>0.1) than those without effusion. Further, inhalant anesthesia caused more changes in the false negative ears (63.63%) than in those with effusion having positive test before anesthesia (12.90%) (P<0.001). Conclusions: From the data of this study, it could be said that reflectivity shows changes according to the amount of effusion which is in contact with the tympanic membrane under anesthesia, and that curve angle becomes more sensitive to detect effusion when anesthetic gas diffuses into the middle ear with effusion, probably due to the pushing of effusion towards the tympanic membrane. © 2003 Elsevier Science Ireland Ltd. All rights reserved.