We compared the postoperative evolution of patients in whom an ileoanal anastomosis was performed, with (group 1, n:9) an without (group 2, n:7) an ileal reservoir. 3 of the 9 patients in group 1 developed intractable diarrhea, it was necessary to reoperate these children and to construct an ileal reservoir. It was not necessary to reoperate any of the group 2 patients; 2 of whom still have an ileostomy due to the presence of preanastomotic abscess. These 2 last patients where excluded from the following analysis. 2 months after surgery, children in group 1 had 16 +/- 2 bowel movements a day, compared with 8 +/- 2 in group 2, p less than 0.05. Children in group 1 did less well than those in group 2 when the following parameters were compared: fecal incontinence (7/9 vs 0/5), perianal dermatitis (6/9 vs. 1/5), treatment with antidiarrheal agents (5/9 vs 0/5), missing school (4/9 vs 0/5) and diminished social activities (4/9 vs 0/5). We conclude that in children who require colectomy, better results are obtained when an ileoanal anastomosis with ileal reservoir is performed.