The objective of this study was to evaluate the efficacy of warming devices in patients undergoing open abdominal surgery in lithotomy position. This randomized, controlled trial was designed to compare body temperatures of patients undergoing open abdominal surgery in lithotomy position between February and May 2019. After prewarming for 30 min with forced-air using a full-body blanket, patients were randomized to receive intraoperative warming either with forced-air using a blanket covering the upper torso and upper extremities in combination with circulating-water-mattress warming the back (Group I) or with only forced-air using blanket covering the upper torso and upper extremities (Group II). Primary outcome measure was the intraoperative change in core-body temperature using oesophageal temperature probe. A total of 28 patients were randomized. The mean core-body temperatures (Group I: 36.1 SD0.41 vs Group II: 35.9 SD0.53 degrees C; p=0.139) and intraoperative changes (Group I: 0.41% vs Group II: -0.001%; p=0.306) were similar. The core-body temperature at the end of the operation correlated with the operating room temperature in Group II (r=0.862, p<0.001), but not in Group I (r=0.323, p=0.259). The combination of forced-air warming and circulating-water-mattress for open abdominal surgery in the lithotomy position may be more beneficial than forced-air warming alone, due to maintenance of the intraoperative mean core-body temperature >= 36 degrees C, despite variations in operating room temperature.