HYPOTHERMIA resulting from anaesthesia is common in the perioperative period and may increase the risk of cardiac arrhythmias and other complications. Very small animals are especially at risk of developing hypothermia because of their larger surface area to volume ratio compared with heavier animals. If the bodyweight of an animal is abnormally low, heat loss may also be increased due to less body fat insulation. The risk of hypothermia can be reduced by a variety of methods and many devices are available to provide warmth for anaesthetised animals. This article discusses why temperature loss is important, and how its effects can be minimised.