OBJECTIVE To study the incidence of hypoxaemia and bradycardia in children who undergo guillotine adenotonsillectomy in a sitting position, without intubation and under inhalation anaesthesia. DESIGN Retrospective study. METHOD Analysis of age, weight, sex, oxygen saturation, heart rate and subsequent bleeding in all children up to the age of 11 years who underwent guillotine adenotonsillectomy in the period December 1999 to December 2007. Hypoxaemia was defined as oxygen saturation of less than 85% for longer than 60 s. Bradycardia was defined as a heart rate of less than 60/min for longer than 30 s. RESULTS We analysed data from 2963 patients. The mean age was 4.7 years and mean weight 18.8 kg. There was no significant relationship between age, weight and the onset of incidental desaturation or bradycardia. A total of 132 patients (4.5%) had hypoxaemia and 280 patients (9.4%) had bradycardia. Twenty-five patients had both hypoxaemia and bradycardia, of whom 3 (0.1%) had bradycardia immediately following hypoxaemia. In none of the recorded episodes of hypoxaemia and bradycardia did this lead to peri- or postoperative complications. CONCLUSION Hypoxaemia and bradycardia occurred during guillotine adenotonsillectomy in non-intubated children in a sitting position under inhalation anaesthesia. The simultaneous onset of hypoxaemia and bradycardia is rare, however, and does not lead to perioperative complications. A further study is required using adenotonsillectomy with a large number of intubated and non-intubated children in order to compare the incidence of hypoxaemia and bradycardia and the occurrence of complications.