Spirometry with incentive games was applied to 207 2-5-year-old preschool children (PSC) with asthma in order to refine the quality-control criteria proposed by Aurora et al. (Am J Respir Crit Care Med 2004;169:1152-159). The data set in our study was much larger compared to that in Aurora et al. (Am J Respir Crit Care Med 2004;169:1152-159), where 42 children with cystic fibrosis and 37 healthy control were studied. At least two acceptable maneuvers were obtained in 178 (86%) children. Data were focused on 3-5-year-old children (n = 171). The proportion of children achieving a larger number of thresholds for each quality-control criterion (backwardextrapolated volume (Vbe), Vbe in percent of forced vital capacity (FVC, Vbe/FVC), time-to-peak expiratory flow (time-to-PEF), and difference (Δ) between the two FVCs (ΔFVC), forced expiratory volume in 1 sec (ΔFEV1), and forced expiratory volume in 0.5 sec (ΔFEV0.5) from the two “best” curves) was calculated, and cumulative plots were obtained. The optimal threshold was determined for all ages by derivative function of rate of success-threshold curves, close to the inflexion point. The following thresholds were defined for acceptability: Vbe ≤75 ml and ≤10% of FVC, time-to-PEF <120 msec, and repeatability: ΔFEV1, and ΔFEV0.5 <110 ml and ≤10% of best effort, and ΔFVC ≤100 ml and ≤12.5%. These were obtained in 85%, 93%, 94%, 90%, and 89% of children, respectively. For practical reasons, we suggest choosing the same threshold for all repeatability criteria, i.e., ΔFVC, ΔFEV1, and ΔFEV0.5 ≤110 ml and ≤10%. In conclusion, a majority of PSC with asthma can perform at least two acceptable maneuvers. Acceptability and repeatability criteria defined in a larger data set can be applied to preschool children. Spirometry could therefore be used to assess respiratory function in preschool children with asthma.