Snoring is a common occurrence in children listed for adenotonsillectomy. This may be associated with obstructive sleep apnoea syndrome, in which case the post-operative recovery of these children needs to be closely monitored. This study undertakes to assess whether an overnight pre-operative pulse oximetry can determine the need for high dependency unit (HDU) observation of these children after their operation. It is a retrospective study identifying patients from the high dependency unit admissions register over a two-year period. It was noted in which of these patients a pre-operative pulse oximetry was actually done and how it related to the post-operative overnight pulse oximetry in terms of desaturation events. The study involved 82 patients who underwent elective adenotonsillectomy, adenoidectomy or tonsillectomy for obstructive sleep apnoea syndrome (OSAS). In 59% of these patients pre-operative overnight pulse oximetry was performed and 32 were considered high risk. Thirty patients showed oxygen desaturation events. It was observed that all children who showed desaturation events pre-operatively also exhibited this in the post-operative pulse oximetry monitoring. Other children, for whom HDU was arranged post-operatively on clinical grounds but who had not undergone pre-operative overnight pulse oximetry, also showed desaturation events in SaO2 monitoring in the post-operative phase. The authors therefore highly rate the value of pre-operative overnight pulse oximetry in predicting post-operative desaturation events and suggest that this simple investigation be carried out in all children in whom OSAS is suspected so that the need for HDU may be identified. This may be a useful predictor for HDU bed requirement allowing targeted referrals for an increased level of post of care.