Introduction of air into the arterial circulation can cause cerebral air embolism, leading to severe neurological deficits. A case is reported on a patient suffering from fatal cerebral air embolism after a subclavian vein catheter had been inserted. The risks associated with inserting and removing central venous catheters are described. Apart from the pathogenesis of a paradoxical air embolism in a patient with a right-to-left shunt due to a patent foramen ovale, air embolism can occur if a large amount of air traverses the pulmonary circulation. The ability of the pulmonary vasculature to filter air may be exceeded by a bolus injection of more than 30 ml air. Air embolism is suspected if acute neurological symptoms occur after inserting a central venous catheter. Echocardiography, especially transoesophageal echocardiography. Is highly sensitive in detecting air emboli in the ventricles. Treatment is effected with hyperbaric oxygen and standard measures of intensive-care medicine.