Pulse oximetry (PO) was applied to 79 otherwise healthy children during and after minor ENT surgery under general anaesthesia in private practice. The PO data were not available to the anaesthetist unless desaturation to less than or equal to 85% was present for greater than or equal to 30 s. This occurred in 12 and 9 cases during anaesthesia and recovery, respectively, only 8 and 5 cases, respectively, being diagnosed clinically. Desaturation during and after anaesthesia was more common in children undergoing adenoidectomy than during procedures for which endotracheal intubation was not performed. During recovery, desaturation was more likely to occur in the same patients again. Lower values of SaO2 were found in younger children and in children resisting or crying at induction. There was a (weak) negative correlation between SaO2 and HR. As clinically undiagnosed desaturation occurs even in healthy children undergoing minor surgical procedures, a more widespread use of PO during and after anaesthesia may be advisable.