In order to establish liability there must be a causal connection between an objectively erroneous action and the ensuing damage. Criminal negligence presupposes that failure on the part of the anaesthetist to exercise the necessary care, including neglect properly to choose and supervise his assistants, is responsible for the mishap. Since anaesthesia constitutes a trespass to a person's body the consent of the patient has to be obtained. Such consent is valid only if the patient has been apprised of the nature, significance and risks of the anaesthetic method to be used. The anaesthetist must inform the patient whether general or regional anaesthesia is planned. The extent to which such information must be supplied and proof that it has been given may present difficulties. A practical approach is to provide the patient with as much information as will enable him to ask relevant questions and then to decide whether or not he wants further explanations.