The impulse oscillation system (IOS) measures respiratory impedance (Zrs) in terms of resistance (Rrs) and reactance (Xrs) at multiples of 5 Hz. These measurements can be used clinically to help diagnose and monitor respiratory disorders, independent of effort. There is, as yet, no information on reference values for IOS in Iranian adolescents.The predictive equation for resistance and impedance at 5 and 15 and 25 Hz, for the first time, in 509 Iranian adolescent subjects (265 boys (aged 6-19 years) and 253 girls (aged 5-19 years) were determined. Gender-specific linear prediction equations were developed by multiple regression analysis; with measuring (R5, R15, R25, X5, X15, X 25) as dependent variables regressed against age (A) and height (H).For both genders, age and height had negative effects on resistance, while age and height had a positive effect on reactance. The prediction equations for R5 and X5 are as follows: R5: -1.35x10(-5) x agex2.823 - 0.001 x height x1.022 + 0.547 for girlsX5: 1.78x10(-7)x age x1.08 + 0.002 height x4.150 - 0.539, for girls R5: -6.19x10(-7)x age x 3.820 - 6.78E-005 x height x1.651 + 0.691 for boysX5: 6.95x10(-23) x age x16.226 + 0.004 height x 0.846- 0.430, for boys, respectively. Our results therefore provide an original frame of reference for R5, R15, R25, X5, X15, X25 in Iranian adolescents population, obtained from a standardized forced oscillation technique.