Patients undergoing surgery are prone to develop pressure ulcers during the surgical procedure. The aim of the study was to gain insight into the problem by describing the incidence, clinical features and progression of pressure ulcers and closed pressure ulcers in patients undergoing surgery lasting more than 4 hours. A prospective follow-up study was conducted in a university hospital in the Netherlands. Two-hundred and eight patients from nine surgical specialities were included in the study. The skin of patients was observed the evening before surgery and, if the patient's condition allowed it, directly postoperatively and subsequently daily for 14 days or until discharge, whichever occurred first. When patients developed a pressure ulcer they were observed daily until discharge or until the pressure ulcer had healed. The size and colour of the lesion, stage and skin condition were described every day. In addition, data were collected concerning the operation, postoperative period, and general characteristics. Forty-four patients (21.2%) developed 70 pressure ulcers in the first 2 days following surgery. Twenty-one pressure ulcers deteriorated in the days following surgery. More than half (52.9%) of the lesions developed on the heels, and 15.7% developed in the sacral area. Twenty-five patients (12%) were impaired by the lesions they developed. None of the patients in the study developed closed pressure ulcers. Pressure ulcer development during a surgical procedure is a serious problem. Therefore, preventive measures should be taken during surgery and the first few days afterwards, until the patient is able to mobilize independently.