Abstract Gastroesophageal reflux (GER) frequently complicates the clinical course of children suffering from conditions leading to upper airway obstruction (UAO) (choanal atresia, tracheomalacia, esophageal atresia, vascular rings, etc). In an attempt to explore whether partial airway obstruction causes changes in the normal thoracoabdominal pressure gradients, we measured end-inspiratory intrathoracic and intraabdominal pressures in anesthetized rats under spontaneous breathing conditions, after tracheostomy, and under upper airway obstruction induced by tracheal intubation with three progressively narrower cannulae (inner diameters 1.0 mm, 0.5 mm, and 0.2 mm). We also measured the lower esophageal sphincter pressure (LESP) and length (LESL) and calculated the thoracoabdominal end-inspiratory pressure gradient (TAEIPG). Neither LESP nor LESL changed significantly before or after maximal tracheal obstruction (14.3 ± 6.2 v 18 ± 7.6 cm H 2 O [ P > .05] and 0.34 ± 0.09 v 0.41 ± 0.1 cm H 2 O [ P > .05] respectively) but TAEIPG significantly increased from 5.58 ± 1.34 cm H 2O to 17.62 ± 4.27 cm H 2O ( P < .01) under the same conditions, mainly as a result of progressively increasing negative intrathoracic pressures during inspiration. These experiments prove that the powerful thoracoabdominal pressure gradients developed after partial UAO may contribute to the pathogenesis of GER by overcoming the antireflux barrier function. This study points out the convenience of routinely screening for GER all children with airway obstructive conditions, bearing in mind that the reestablishment of normal respiratory conditions should be the primary goal of treatment.