To determine the risks of reoperation and clinical recurrence in Crohn's disease involving the colon, we analyzed by both crude and actuarial (life-table) methods follow-up data from 160 patients hospitalized with Crohn's colitis or ileocolitis from 1964 through 1973. A total of 100 patients (63 per cent) underwent major operation; of these, 58 required reoperation. By the 15th year after initial operation, there was a cumulative reoperation rate of 89 and an overall clinical recurrence rate of 94 per cent. Crude data implied that the reoperation rate diminished with each succeeding operative procedure, from 58 per cent after the first operation to 47 per cent after the fourth. By contrast, actuarial analysis revealed that at the three-year follow-up point, the cumulative chance of reoperation increased from 37 per cent after the first surgical procedure to 60 per cent after the fourth. The inexorable tendency of Crohn's ileocolitis to require repeated operations is demonstrable by actuarial methods.