Objective: To determine whether operators with less than 3 months' formal anaesthesiology training have higher rates of complications when performing endotracheal intubation (ETI) in the intensive care unit than operators with longer formal anaesthesiology training. Design and setting: Prospective, single-centre, observational study of consecutive ETIs performed in a general, urban, tertiary ICU between May 2005 and May 2008. Data were collected by self-reported, written questionnaire. Participants: The two pre-defined study cohorts were ETIs performed where the initial operator had less than 3 months' formal training in anaesthesiology, and those where the initial operator had 3 months' or longer training. Main outcome measures: The primary outcome measure was the number of ETIs where one or more pre-defined complications occurred as a result of the ETI. Secondary outcome measures were the number of Ells where one or more respiratory, cardiovascular or trauma complications occurred as a result of the ETI, and the number where the airway was deemed difficult by the operator. Results: Data were collected on 276 ETIs. There were no significant differences in primary or secondary outcome measures between the two main study groups. Operators with less than 3 months' formal training in anaesthesiology had a higher level of medical supervision or assistance (75% v 29%, P<0.001), more favourable patient pre-intubation oxygen saturation on pulse oximetry (Spo(2)) (76% v 65% had Spo(2)>89%, P=0.05), and easier resultant grade of intubation (70% v 56% of intubations were Grade I, P = 0.04), but required more operators (19% v 3% required two operators, P<0.001), and more attempts before ETI was successful (62% v 82% of intubations were successful on first attempt, P<0.001). Conclusion: ETIs performed in the ICU where the initial operator has less than 3 months' formal training in anaesthesiology appear not to be associated with more complications. However, this may be attributable to less experienced operators having more assistance and supervision, and to patient selection.