Neurosurgery in the sitting position not only puts a strain on the cardiopulmonary system, but also carries the risk of venous air embolism. Special monitoring procedures as well as prophylactic measures greatly contribute towards the safety of the patient. The pathogenesis, pathophysiology and the symptoms of venous air embolism are reviewed, and various monitoring methods are discussed, with special reference to their reliability, sensitivity and practicability. The analysis shows that the Doppler ultrasound method, continuous capnography during the duration of the operation, intra-arterial measurement of blood pressure, recording of the central venous pressure and of electrocardiographic changes are essential means of routine monitoring. Suspected air embolism must be promptly dealt with not only by ligation of the severed vein but also by attempts at aspiration of the air bubbles via the atrial catheter. The latter, therefore, plays an important role both as a diagnostic parameter and a therapeutic agent. Although the suggested prophylactic measures do not absolutely protect against complications they will markedly reduce the incidence of venous air embolism.