Background: Children with asthma, even those with severe persistent disease, can have forced expiratory volume in 1 second (FEV ) values ≥100% of predicted, while others have diminished FEV . Objective: We sought to characterize the lung mechanical properties underlying these two asthma phenotypes and the mechanisms explaining the paradox of severe asthmatic children, whom when clinically stable can have an FEV >100% of predicted, but during an acute bronchospastic episode can experience a life-threatening asthma event. Methods: Lung mechanics were evaluated in three groups of children: asthmatics with FEV ≥100% (HFEV ; n = 13), asthmatics with FEV ≤80% (LFEV ; n = 14) and non-asthmatic controls (n = 10). A linear mixed model was used to examine the relationship between volume and static transpulmonary pressures obtained at total lung capacity (TLC); actual TLC %of predicted and flow; and static transpulmonary pressure and flow. Results: HFEV asthmatics had larger airways (FEV z-scores 1.12 vs −2.37; P