The incidence of iatrogenic air embolism can only be estimated since many accidents are not recognized. Clinical manifestations, essentially neurological or cardiovascular disorders vary greatly. Air embolism may occur during coronary or cerebral arteriography, cardiopulmonary bypass, venous catheterism, various types of surgery or blood transfusion among other situations. Once air has entered the arterial circulation, the bubble of gas follows the blood flow until it is blocked by a smaller calibre vessel. The progressive diffusion of the air reduces the size of the embolus which then migrates on to smaller and smaller vessels. Subsequent pathological manifestations of air embolism result from mechanical obstruction leading to ischemia and inflammatory reactions to air acting as a foreign body. The sudden onset signs of neurological impairment with or without a cardiopulmonary component in patients in a high-risk situation leads to clinical diagnosis. Treatment must be started immediately although brain CT scan or echocardiography may help confirm the diagnosis. The source of the air must be immediately identified and removed and the vital functions controlled. Mechanical or facial mask ventilation with pure oxygen is indicated. Hyperbaric oxygen therapy should be instituted. Morbidity and mortality after iatrogenic air embolism is high but major improvements have been achieved with oxygen therapy. Neurological sequellae have been estimated to reach 19 to 50% of the patients. A personal controlled prospective study revealed 14% mortality after hyperbaric oxygen therapy given within 12 hours of the accident.