Abstract Anaesthesia is a necessary part of any operation and it carries with it certain risks to the patient. While every effort can be made to avoid errors secondary to human and system failures, complications can arise, whether they are idiosyncratic reactions, common side effects or unpredictable problems. For the anaesthetist to be able to adequately consent the patient for anaesthesia they must be aware of the risks. This article outlines the risks associated with the conduct of anaesthesia, from preparation and induction to emergence and postoperatively. We look at both general and regional anaesthesia and have given incidence data where they are available. It is not possible to list every possible complication that could occur during an anaesthetic, so we have focused on those that are common and those that are serious (in terms of potential outcome for the patient) and some other relevant procedural issues.