Preoperative investigations, when used to screen for disease not clinically evident, have been shown to be unnecessary. The aim of this study was to rationalize the ordering of preoperative investigations by introducing guidelines and screening all investigations ordered at a new Day of Surgery Admissions clinic. Two hundred and one elective general and ear, nose and throat (ENT) patients attending this clinic at Sir Charles Gairdner Hospital from July to September 1997 were induced in a prospective study group. These were compared to a retrospective control group of 168 elective general and ENT surgical patients who had been admitted for surgery during May to July 1996. Patient demographics were similar for both groups. There were also similar proportions of each surgical subtype and degrees of surgical complexity in each group. There were significant reductions in most types of investigations (electrocardiogram, chest X-ray, liver function tests, urea and electrolytes, full blood examination, coagulation profile) ordered with the Day of Surgery Admissions clinic intervention. This resulted in an estimated reduction of preoperative investigation costs by 38%. It was concluded that the clinic intervention was associated with a reduction in indiscriminate preoperative investigation ordering patterns.