The utility of obtaining routine preoperative laboratory (lab) screening tests was evaluated for a 1-year period in general surgery clinic patients undergoing ambulatory surgical procedures at a teaching hospital. This study sought to determine whether those lab tests not indicated by patient history or physical examination would identify abnormalities that might influence perioperative care of the ambulatory surgical patient or predict perioperative complications. The charts of 142 patients undergoing 155 procedures were reviewed. A total of 300 tests were ordered, with 92 (30.6%) being abnormal. Of the 125 tests indicated, 54 (43.2%) were abnormal, whereas in those lab tests not indicated, 38 (21.7%) were found to be abnormal. In four instances, an abnormal lab test (4 out of 300) result was clinically significant (1.3%), causing cancellation of the surgical procedure in two cases (both indicated lab tests) and diagnosis of urinary tract infection in two patients (both routine urinalyses). Forty-eight of the 142 patients had no preoperative lab tests ordered (34%), with no perioperative complications resulting. Patient charges totaled $15,725 for all lab tests ordered, with $8,573 in charges attributed to those tests not indicated. If lab tests for all general and subspecialty surgical outpatients had been ordered as dictated by patient medical history and physical examination rather than by either routine or by arbitrary criteria, our medical facility could have potentially reduced patient charges by more than $400,000 in the year reviewed, assuming a 52.4 per cent savings as noted above, with no expected adverse outcomes.