The LMA Supreme is a new extraglottic airway device which brings together features of the LMA ProSeal, Fastrach and Unique. We test the hypothesis that ease of insertion, oropharyngeal leak pressure, fibreoptic position and ease of gastric tube placement differ between the LMA ProSeal and the LMA Supreme in paralysed anesthetised patients. Ninety-three females aged 19-71 years were studied. Both devices were inserted into each patient in random order. Two attempts were allowed. Digital insertion was used for the first attempt and guided insertion for the second attempt. Oropharyngeal leak pressure and fibreoptic position were determined during cuff inflation from 0 to 40 ml in 10 ml increments. Gastric tube insertion was attempted if there was no gas leak from the drain tube. First attempt and overall insertion success were similar (LMA ProSeal, 92% and 100%; LMA Supreme 95% and 100%). Guided insertion was always successful following failed digital insertion. Oropharyngeal leak pressure was 4-8 ml higher for the LMA ProSeal over the inflation range (p < 0.001). Intracuff pressure was 16-35 cm higher for the LMA ProSeal when the cuff volume was 20-40 ml (p < 0.001). There was an increase in oropharyngeal leak pressure with increasing cuff volume from 10 to 30 ml for both devices, but no change from 0 to 10 ml and 30-40 ml. There were no differences in the fibreoptic position of the airway or drain tube. The first attempt and overall insertion success for the gastric tube was similar (LMA ProSeal 91% and 100%; LMA Supreme 92% and 100%). We conclude that ease of insertion, gastric tube placement and fibreoptic position are similar for the LMA ProSeal and LMA Supreme in paralysed, anaesthetised females, but oropharyngeal leak pressure and intracuff pressure are higher for the LMA ProSeal.