An incidence of postoperative infection of up to 15 percent has been reported following middle ear ventilation tube surgery. This rate of complication would be considered unacceptable following most other operative procedures. A controlled prospective study of 107 children undergoing tympanostomy and tube surgery over a 1-year period was undertaken. Subjects were randomly assigned to receive antibiotic-steroid otic drops at the time of surgery and for 1 week afterward, oral ampicillin for 24 hours preceding and 3 days following surgery, or no prophylactic treatment.The overall infection rate within four weeks of surgery was 12 percent. Purulent otorrhea occurred in 18 percent of those receiving no prophylactic treatment, in 13 percent receiving ampicillin, and in 6 percent receiving antibiotic-steroid otic drops. Postoperative infection was related to preoperative history of status otitis media and to previous placement of ventilation tubes.