Paramedics provide life-saving emergency medical care to patients in the outof-hospital setting, but only selected emergency interventions have proved to be safe or effective. Endotracheal intubation (the insertion of an emergency breathing tube into the trachea) is an important and high-profile procedure performed by paramedics. In our study population, we found that errors occurred in 22 percent of intubation attempts, with a frequency of up to 40 percent in selected ambulance systems. These findings indicate frequent errors associated with this life-saving technique. These events might be emblematic of larger issues in the structure and delivery of out-of-hospital emergency care. (EMS) to patients suffering life-threatening conditions such as cardiac arrest, respiratory failure, and major trauma. Paramedics often must perform endotracheal intubation (ETI), the insertion of a breathing tube into the trachea (windpipe), on these critically ill patients. Intubation is regarded as one of the most important EMS procedures and has been the standard of care in the United States for more than twenty years. 1 ETI is a complex procedure. Considerable skill is required to maneuver the breathing tube into the correct position. An improperly placed tube (for example, in the esophagus) can deprive the patient of oxygen and rapidly lead to death. Physician trainees in anesthesiology, critical care medicine, and emergency medicine spend many hours in controlled settings learning and practicing this difficult procedure. In contrast, paramedics undergo only a fraction of the training in ETI that physicians receive. Furthermore, paramedics perform ETI in uncontrolled, stress-