BACKGROUND Paediatric obstructive sleep apnoea is a common clinical condition managed by most ENT clinicians. However, despite the plethora of publications on the subject, there is wide variability, in the literature and in practice, on key aspects such as diagnostic criteria, the impact of co-morbidities and the indications for surgical correction. METHODS A systematic review is presented, addressing four key questions from the available literature: (1) what is the evidence base for any definition of paediatric obstructive sleep apnoea?; (2) does it cause serious systemic illness?; (3) what co-morbidities influence the severity of paediatric obstructive sleep apnoea?; and (4) is there a medical answer? CONCLUSIONS There is a considerable lack of evidence regarding most of these fundamental questions. Notably, screening measures show low specificity and can be insensitive to mild obstructive sleep apnoea. There is a surprising lack of clarity in the definition (let alone estimate of severity) of sleep-disordered breathing, relying on what may be arbitrary test thresholds. Areas of potential research might include investigation of the mechanisms through which obstructive sleep apnoea causes co-morbidities, whether neurocognitive, behavioural, metabolic or cardiovascular, and the role of non-surgical management.