Two thousand sixty-three surgical procedures were performed on 1992 patients (1715 dogs and 277 cats). In a retrospective analysis, the procedures were categorized according to the expected degree of wound contamination, and corresponding wound infection rates were determined. The number of procedures in each category and the percent that became infected were as follows: clean (1100, 2.5%), clean-contaminated (554, 4.5%), contaminated (172, 5.8%), and dirty (237, 18.1%). The administration of antibiotics significantly reduced the frequency of wound infection in clean surgical procedures performed by senior veterinary students (p less than 0.05), but not in clean elective procedures performed by faculty or resident surgeons that required 90 minutes or less to complete. There was a significant correlation between elevation of rectal temperature postoperatively and increased duration of the surgical procedure. However, the rectal temperature measured the day after surgery was not an accurate predictor of wound infection.