The aims of this retrospective sutdy were to assess the incidence of infection after periodontal surgery, in relation to the type of surgical procedure, and the effectiveness of prophylactic tetracycline administration. Nineteen (4.4%) of 445 surgical procedures in patients who were given no tetracycline resulted in signs of infectioon, while two (3.8%) in patients who were treated with tetracycline resulted in signs of infection. There was no statistically significant difference between these incidences, suggesting that there is no reason for routine tetracycline prophylaxis in periodontal surgery. There was no statistically significant difference in the incidence of infection whether or not bone (ostectomy or osteoplasty) or tooth extraction was involved in the surgical procedure.