Objective: The purpose of this study was to identify risk factors contributing to pressure ulcer development in patients undergoing scheduled, prolonged operative procedures. Design: A descriptive study was conducted. Setting and subjects: A large university teaching facility provided the setting. Thirty-three subjects who underwent operative procedures lasting longer than 10 hours, as determined from the daily operating room schedule through a 6-month period, were included in the study. Instruments: Braden Scale for Predicting Pressure Sore Risk was used before the operation. Visual skin inspection, preoperative interventions, and demographic information were documented with a data-collection tool. Postoperative skin breakdown and its severity were assessed as stage I through IV according to the Pressure Ulcer Classification System recommended by the National Pressure Ulcer Advisory Panel. Methods: Visual preoperative skin assessment was performed and the Braden Scale was completed in the operating room holding area. Demographic information was collected from patient interviews and the medical record. Patient positioning and the placement of all positioning and thermal devices were observed and recorded in the operating room. Within 48 hours after the surgical procedure, the patients' skin was visually inspected. Pressure ulcers were noted, staged, and recorded. Main outcome measures: The χ 2 analyses compared those who did and those who did not acquire pressure ulcers for differences in gender, type of operation, position used in the operating room, and types of positioning devices. Student's t tests compared those who did and did not acquire pressure ulcers for differences in age. Braden Scale score, number of positioning devices, and length of operation. Results: Of the 33 patients studied, 15 (45%) were found to acquire stage I or II pressure ulcers within 48 hours after their procedure. Of the 15 patients who acquired pressure ulcers, 75% were placed on a warming blanket during the procedure. This was the only significant finding among the risk factors investigated in the comparison of those who did and did not acquire pressure ulcers ( χ 2 = 4.3, p < 0.05). Conclusions: Removal of the warming blanket from routine intraoperative use with patients undergoing prolonged operations is indicated. Continued follow-up of this patient population will help to determine whether avoidance of warming blankets is sufficient to lower the incidence of pressure ulcer formation.