Both effects of anaesthesia and analgesia are involved in the anaesthesia risk. Most often, anaesthetic accidents appear to be related to hypoxia. Applying anaesthetic security principles allow controlling risk. Systematic use and check of monitoring instruments and anaesthesiology department organisation appear as major preventive measures. Independent operative risk is related to individual, surgical and anaesthetic factors, which interact with one another. Individual preoperative evaluation is one of the great challenges of anaesthesiology. The establishment of an aimed perioperative anaesthetic strategy is the best warrant of the operative risk reduction. Assessment of individual benefit to risk ratio takes also into account the experience of the surgeon and anaesthesiologist. It implicates the patient's choice as well his general practitioner as a privileged advice.