The forced oscillation technique (FOT) may be affected by the upper airway artifact in children with airway obstruction. The aim was to test the impact of the artifact on FOT ability to diagnose asthma in children as recommended by current guidelines. Methods: The FOT was performed in 58 asthmatics and 27 controls before and after salbutamol. Respiratory resistance (Rrs) was measured at 8 Hz with a standard generator (SG), and a head generator (HG) that minimizes the upper airway artifact. The response to salbutamol was computed as change in respiratory resistance (Δ%Rrs) and admittance (Δ%Ars) that almost cancels the effect of the upper airway artifact. Results: Rrs and Δ%Rrs were significantly larger in patients than controls by HG (respectively P < 0.001 and P = 0.002) but not SG, while Δ%Ars was larger in asthma than control by both (P < 0.04). Best discriminators between patients and controls were Rrs or Δ%Rrs by HG and Δ%Ars by SG. Conclusion: In asthmatic children, the upper airway artifact significantly impacts FOT measurements. The diagnostic value may be improved by minimization of the shunt, such as the computation of Δ%Ars.