OBJECTIVE: To compare the effectiveness of traditional and online teaching methods for educating anesthesiology residents in the principles and practice of difficult airway management. DESIGN: Prospective, randomized, controlled trial. SETTING: University hospital. PARTICIPANTS: Two randomly selected groups, each containing 28 physicians enrolled from among residents in Anesthesiology and Intensive Care Medicine in Italy. INTERVENTIONS: Residents in Group 1 took a traditional 5-h course on the principles and practice of airway management, which included lectures, slide projection, and dummy demonstrations. The same material was presented to Group 2 in an exclusively online format, which could be individually accessed for a period of 36 h. In the online course, student-instructor interaction was provided through threaded discussion forums during three 30-min real-time question-and-answer sessions. MEASUREMENTS AND RESULTS: Differences in baseline and post-course scores on written tests and practical skills tests were measured. Knowledge gains in Group 2 were slightly, but not significantly, greater compared with Group 1 both in written (P=0.228) and practical skills (P=0.376) tests. Semi-quantitative ratings of learner satisfaction were significantly higher in the online group (P=0.014). Almost all online students (93%) were logged in for at least 45 of the 90 min of real-time question-and-answer sessions. The four instructors spent an average of 144+/-10 min preparing answers and interacting with online students. CONCLUSIONS: Online teaching formats may be a valid alternative for teaching residents the principles and practice of difficult airway management. Interaction with instructors seems to be an important element, but it may require substantial time commitments by instructors.