Statewide hospital discharge data in South Carolina for the period 1979-81 were used to evaluate the effectiveness of the incidental appendectomy performed as a preventive measure. The occurrence of incidental appendectomy exceeded that of appendicitis treated by appendectomy, with population-based rates of 1.13/1,000 and 0.97/1,000 person-years, respectively. Over 64 per cent of appendicitis cases occurred in persons under 25 years of age while 74 per cent of incidental appendectomies occurred in persons age 25 and over. Extrapolating to the nation, the data suggest that 254,250 incidental appendectomies might prevent 3,382 future cases of hospitalized appendicitis. The cost of the prevented cases is estimated as $6,764,000. The cost of the incidental appendectomies would be $20,340,000 if as many as 10 per cent of surgeons' fees were separately charged and twice as much if twice as many were so charged. Information on charges for incidental appendectomies is not readily available.