Sevoflurane prolongs the QT interval (QTI). Patients with congenital sensorineural hearing loss (SNHL) often have a prolonged QTI. This study was to investigate the effects of sevoflurane on the QTI in SNHL and control children. Thirty patients with SNHL and 30 controls were studied. The corrected QT interval (QTc), interval from peak to end of T wave (Tp-e) and QT variability index (QTVI) were analysed. QTc and Tp-e were estimated by the average QTc and Tp-e measured beat-by-beat for 15 min. Heart rate power spectral analysis was performed. In both groups, QTc and QTVI increased during anaesthesia, but Tp-e did not change. There were no differences in QTc, QTVI, Tp-e, low- and high-frequency power between the two groups. In both groups, sevoflurane lengthened the QTc and QTVI intervals but not Tp-e.