A follow-up study of 27 children operated for congenital duodenal obstruction (CDO) in the years 1953--71 is presented. Nine children belonged to the intrinsic and 18 children to the extrinsic group of CDO. A total of 7 retrocolic, isoperistaltic, side-to-side duodeno-jejunostomy, 7 Ladd's operation, 8 duodenolysis, 2 reduction of midgut volvulus, 2 duodenostomy a.m. Morton and one gastro-jejunostomy were performed at the age of 1 day--15 years. The clinical and radiological examinations were performed 3--21 years (mean 10 years 2 months) after these operations. In 3 cases there was a moderate duodenal dilatation, but reoperation was not necessary. During the follow-up period, one boy, now aged 8 years, developed a blind pouch-syndrome in the I portion of the duodenum containing a 5 x 5 cm phytobezoar 4 1/2 years after duodeno-jejunostomy. The frequency of blind pouch-syndrome after duodeno-jejunostomy was thus 1:7 or 14%. One girl, now aged 9 years, developed a blind loop-syndrome in the ileocaecal segment 3 months after side-to-side ileotransversostomy, which was performed from adhesion-obstruction after duodenolysis for malrotation I and CDO. Both the blind pouch- and the blind loop-deformation were resected and the children recovered well. To avoid blind-pouch- and blind loop-deformations in the intestines, the anastomosis must be made wide enough, and especially in the surgery of the jejuno-ileo-colic region an end-to-end anastomosis is preferable.