Inclusion Criteria:  Consecutive patients < 18 years, admitted to participating hospitals during the study period elective and non-elective surgery (including day case surgery) operative procedures outside operating theatres where a general anaesthetic (GA) is performed.  Exclusion Criteria:  radiological or other procedures not requiring general anaesthesia, or where general anaesthesia is performed but no procedure is performed e.g. general anaesthesia during magnetic resonance imaging (MRI). Obstetric surgery. Prior participation in ASOS-Paeds.