Twelve head and neck cancer patients scheduled to undergo an operation contaminated by entrance into the upper aerodigestive tract were enrolled in a prospective, randomized, double-blinded study to evaluate the efficacy of a preoperative antibiotic mouthwash in reducing oral cavity quantitative bacterial counts and the incidence of postoperative wound infections. The group who received the antibiotic mouthwash had a large reduction in the bacterial counts, whereas the group who received the placebo mouthwash had an increase in the bacterial counts (p = 0.024). None of the patients who received the antibiotic mouthwash had postoperative complications; two of the five patients who received the placebo mouthwash had postoperative complications.