The purpose of this study was to evaluate the ability of preoperative laboratory testing to predict postoperative complications. Five hundred twenty patients undergoing elective surgery had their American Society of Anesthesiologists' classification, ponderal index, electrolyte values, glucose levels, blood urea nitrogen/creatinine values, complete blood counts, coagulation studies, total protein/albumin/lymphocyte count, electrocardiogram, chest radiograph, urinalysis, pulmonary function tests, type of anesthesia, and type of operation recorded preoperatively. Patients were followed prospectively after surgery for the development of complications. The data were analyzed by univariate and multivariate methods. Postoperative complications were strongly associated with American Society of Anesthesiologists' classification, type of anesthesia, and type of operation. However, only a few laboratory tests, such as electrocardiogram, chest radiograph, and nutritional status, were associated with postoperative complications. Therefore, in general, preoperative laboratory testing should only be undertaken for specific indications. Recommendations for routine tests are made depending on the age of the patient.