Upper airway patency can be compromised when children (or adults) receive sedative medication. The study examines the effect of two different positioning techniques (use of the 'sniff position pillow' (SPP) and shoulder elevation (SE) on maintenance of upper airway patency using MRI in 21 children sedated with intravenous pentobarbital (5-8 mg.kg-1). Children positioned on the SPP had a significantly greater degree of atlanto-occipital extension (P < 0.05), and a significantly greater nasopharyngeal diameter (P < 0.05) than those with shoulder elevation. The degree of atlanto-occipital extension was not significantly correlated with pharyngeal diameter (R = -0.68). No clinical signs of upper airway obstruction were noted and oxygen desaturation did not occur. Both positioning techniques were consistently associated with upper airway patency under the study conditions described. In obligate nose breathers to whom sedative agents are administered, the SPP is more likely to maintain nasopharyngeal patency than shoulder elevation.