Whilst anesthetic incidents due to problems with the delivery of medical gases to a surgical unit are exceptional, their consequences are potentially drastic. With the growing of modern hospitals, every anesthetist may one day find himself confronted with such events, which are new to him, partly because they are infrequent, but mainly because they are due to causes outside his immediate environment. A simple mistake in the labelling and identification of medical gas lines resulted in a cross-connection of the oxygen and air, causing perioperative hypoxemia following the administration of a mixture poor in oxygen. The questions of training, responsibility and procedures in regard to these types of incidents are discussed below.