Summary Hypothermia after elective cardiac surgery is an important physiological abnormality and is associated with increased morbidity and mortality. The Australian and New Zealand intensive care adult patient database was studied to obtain the lowest and highest temperature in the first 24 h after surgery. Hypothermia was defined as core temperature <36 A?C; transient hypothermia as temperature <36 A?C that was corrected within 24 h; and persistent hypothermia as hypothermia that was not corrected within 24 h. Hypothermia occurred in 28 587 out of a total of 43 158 consecutive patients (66 ) and was persistent in 111 (0.3 ). Transient hypothermia was not independently associated with increased hospital mortality (OR = 0.9, 95 CI 0.8a??1.1), whereas persistent hypothermia was associated with markedly increased risk of death (OR = 6.3, 95 CI = 3.3a??12.0). Hypothermia is common in postoperative cardiac surgery patients during the first 24 h after ICU admission but, if transient, is not independently associated with an increased risk of death.