The management of Meckel's diverticulum (MD) incidentally detected in adults remains controversial. To assess the risk involved in excision of such diverticula and the incidence of complications arising from MD in adult life, we analysed 260 cases of MD found at laparotomy in a baseline population during a 15-year period. There were 148 symptomless and 112 symptom-producing diverticula, with intestinal obstruction as the most common complication. Assuming a 2 per cent general incidence of MD, the complication rate in these adult patients was 0.03 per cent per year. The calculated lifetime risk of complication from MD was 3.7 per cent at age 16 years, falling to zero in old age. Excision of an incidentally detected MD entailed a 6 per cent rate of major complications. Twenty-eight symptomless diverticula were not excised, and follow-up revealed no complications in these cases. In adults an incidentally discovered, symptomless Meckel's diverticulum should be left in place.