SummaryIn a prospective, randomized, single‐blind study of combined pulse oximetry and capnography in 196 children whose anaesthetic was managed by endotracheal intubation we observed 10 patients with 14 episodes of endobronchial intubation (EBI). Pulse oximetry provided the first diagnostic clue in 13 events; the one event first diagnosed by capnography was also accompanied by oxygen desaturation. Two EBI occurred immediately after the initial intubation (‘primary’ EBI). Twelve episodes of EBI in eight patients occurred after correct initial endotracheal tube position (‘secondary’ EBI). EBI gave rise to eight episodes of ‘minor’ desaturation (oxygen saturation (Spo2) ≤ 95%≥ 60 s); four resulted in ‘major’ desaturation (Spo2≤ 85% for 30 s). Only three EBI events produced clinical signs or symptoms. Seven patients were less than 1 year; EBI was not, however, related to age.A high frequency (5.1%) of clinically unrecognized EBI was found in infants and children. A persistent yet small, reduction in oxygen saturation provided the early evidence of secondary EBI in the majority of cases. Clinical signs and capnography proved least effective in the early dia