Purpose: Perioperative hypothermia, a common complication of general anesthesia, is associated with adverse outcomes. While active warming methods are recommended, the effectiveness of circulating-water mattresses during ophthalmic surgeries remains understudied. This randomized controlled trial assessed whether a circulating-water mattress combined with a cotton quilt (Group W) was superior to a cotton quilt alone (Group C) in maintaining patient body temperature during ophthalmic day-case surgery. Patients and Methods: Group W patients (n=39) used a preheated circulating-water mattress (38 degrees C) on the operating table and were covered with a cotton quilt (from their entry to the operating room until they returned to the ward). Group C patients (n=38) lay on an unheated table and were covered with a cotton quilt. The axillary temperature in the surgical waiting area served as the baseline. Axillary temperature, ambient temperature, heart rate, and mean arterial pressure were documented at anesthesia induction (T-0), start of surgery (T-1), every 5 min for the first hour (T-2-T-13), and end of surgery (T-14). Satisfaction and thermal comfort scores were assessed at baseline in the waiting area, 5 min before anesthesia induction (t(0)), 15 min after entering the post-anesthesia care unit (PACU) (t(1)), and upon leaving the PACU (t(2)). The primary outcome measure was the axillary temperature at T-14. Results: At T-14, Group W had a higher axillary temperature than Group C (36.40 +/- 0.06 degrees C vs 36.18 +/- 0.06 degrees C, P=0.011), with the mean difference 0.22 degrees C, which did not exceed the predefined superiority threshold of 0.30 degrees C, indicating that the warming effect in Group W was not superior to that in Group C. However, thermal comfort and satisfaction scores were significantly enhanced at t(0) and t(1) (P< 0.05). Conclusion: During ophthalmic day-case surgeries, a circulating-water mattress plus a cotton quilt was not superior, regarding their warming effect, but they significantly enhanced patients' thermal comfort and satisfaction.