314 patients who had undergone multilevel thoracolumbar spinal surgery were randomized to one of two antibiotic treatment arms: a 24-hour treatment, or treatment for the duration of the postoperative drain. The object of this study was to analyze prospective thoracolumbar spine surgery data obtained from this study to determine the incidence of surgical site infections as defined by the Centers for Disease Control (CDC) criteria. 40 infections meeting CDC criteria were found (infection rate of 12.7%), with half of the infections identified as culture-positive, 37 of 40 cases involving operative fusion, and 20 cases occurring in revisions. The most common organisms by magnitude were Staphylococcus aureus, coagulase-negative Staphylococcus, Propionibacterium acnes, and Escherichia coli.