Perioperative heat loss is a potentially serious complication of surgery in infants. The influence of laparoscopic surgery on perioperative hypothermia has not previously been documented. We reviewed heat loss in 26 infants undergoing laparoscopic pyloromyotomies compared with 42 control patients having the standard open procedure over the same time period. The mean fall in temperature in the laparoscopic group was -0.69 degreesC compared with -0.47 degreesC in the open group. This difference was not significant, with a P value of 0.077. This may reflect the small sample size and the relatively short duration of this procedure with few instrument changes. There was a trend for increased heat loss in the laparoscopic group, which might have implications for longer and more complex laparoscopic procedures in infants.