Over 5 years, 25 severely retarded institutionalized patients accounted for 29 admissions for laparotomy due to acute abdomen. The patients' symptoms were always of short duration, yet 38% of operations were judged to be delayed. This was thought to be due to the patients' inability to communicate and to altered pain sensation. Pica (depraved appetite) accounted for 48% of admissions and perforation was common (41%). The death rate was high (4 (14%) of the 29 admissions and 3 (21%) of the admissions associated with pica). An unexpected high incidence (24%) of peptic ulcer was also seen. Unless the patient was admitted in a state of shock, usual clinical determinations often failed to distinguish early from advanced disease. Young males seem at increased risk and a history of pica is ominous.