In a randomised cross-over study, we compared the performance of the single use i-gel supraglottic airway and reusable classic laryngeal mask airway (cLMATM) in 50 healthy anaesthetised patients who were breathing spontaneously. Primary outcome was successful insertion at first attempt. Secondary outcomes included overall insertion success rate, ease of insertion, leak pressure and fibreoptic position. Success rate for insertion at the first attempt was significantly different (54% with i-gel vs 86% with cLMA; p = 0.001). Overall success after two attempts (when the anaesthetist was allowed to change the size of the device) improved to 84% with i-gel vs 92% with cLMA; p = 0.22. In 14 patients, the i-gel when used first needed to be replaced with a larger size. Leak pressure was higher for the i-gel (median [IQR] 20 [14–24] cm H2O than the cLMA 17 [12–22] cm H2O; p = 0.023). The fibreoptic view through the device was significantly better with the i-gel than the cLMA, which was statistically significant (p = 0.03). We conclude that, with its current sizing recommendations, the i-gel is not an acceptable alternative to cLMA. However because of the significantly improved success rate after a larger sized i-gel was used, we recommend the manufacturer to review the sizing guidelines to improve the success rate.