Objective: Perioperative hypothermia is a common complication of general anaesthesia in children. The primary objective of the study was to detect the occurrence of hypothermia in a group of paediatric patients. The study enrolled paediatric patients aged 0-18 years of age indicated for surgery of estimated duration of more than 30 minutes. The secondary objective was to identify the risk factors for hypothermia. Setting: Department of Paediatric Anaesthesia and Intensive Care Medicine of University Hospital. Materials and methods: Prospective observational monocentric study conducted from the 1st April 2017 to 8th December 2017 at the Department of Paediatric Anaesthesiology and Intensive Care Medicine, University Hospital Brno. We observed the incidence of body temperature below 36.5 degrees C and below 36.0 degrees C Results: Temperature < 36.5 degrees C occurred in 66 % of patients, in the subgroup of patients under one year of age in 73 % and in the neonatal group in 87 %. 36 % of all patients experienced core body temperature under 36.0 degrees C. In the under one year subgroup it was captured in 41 % patients and in the neonatal subgroup we found temperature under 36.0 degrees C in 63 % of cases. We recorded a significantly higher incidence of body temperature below 36.5 degrees C in the subgroup of patiens with opening of a body cavity. We identified the operating theatre temperature as a statistically significant factor. Conclusion: The incidence of perioperative hypothermia under 36.0 degrees C in our paediatric patients was 36%. We identified the groups of patients at the highest risk of perioperative hypothermia: patients undergoing surgery involving body cavity opening and the low-age patient group.