OBJECTIVES: To determine the cost-effectiveness of local insufflation (via a humidifier) of warm humidified CO(WH-CO) compared with standard care in patients undergoing open or laparoscopic colorectal surgery. METHODS: A decision-analytic model was developed to estimate the costs and quality-adjusted life-years (QALYs) associated with open and laparoscopic colorectal surgery from a UK NHS perspective.  WH-CO was compared with no insufflation in open surgery patients and with unheated CO(U-CO) in laparoscopic patients.  Efficacy data were derived from a published randomised controlled trial reporting on the proportion of patients with hypothermia, a US database analysis of hypothermia patients for open surgery, and from an unpublished UK NHS before and after study of laparoscopic surgery patients. Other parameter inputs were obtained from published literature.  Deterministic and probabilistic sensitivity analyses were conducted to assess the robustness of results. Scenario analyses were undertaken to explore structural uncertainty within the model.  RESULTS: The use of WH-CO dominated standard care, as it was both cost saving and generated greater QALYs, for both open and laparoscopic surgery patients over a one year time horizon.  Results varied by the number of patients undergoing surgery per humidifier per year.  Based on 250 patients using the humidifier each year over a five year lifetime of the humidifier, WH-CO dominated no insufflation in open surgery patients in 71% of model iterations and dominated U-CO in laparoscopic surgery in 98% of model iterations.  WH-CO remained the cost-effective treatment option at a willingness-to-pay threshold of £20,000 per QALY throughout all scenario and sensitivity analyses considered, provided 10 or more patients used each humidifier over its life span.  CONCLUSIONS: The analyses conducted suggest that based upon the currently available clinical evidence, WH-CO is a cost-effective use of resources for patients undergoing either open or laparoscopic colorectal surgery within the UK NHS.