The authors reviewed the ultrasonographic images and medical records of 15 consecutive fetuses with dilated loops of bowel distal to the duodenum and determined the prevalence of cystic fibrosis among them. The criteria for dilated bowel loops included both subjective criteria and luminal measurements. Five of the fetuses (33%) had cystic fibrosis. Eleven had bowel obstruction at birth, and four of those 11 (36%) also had cystic fibrosis. One of the four fetuses without bowel obstruction at birth had cystic fibrosis. There were no differences in sonographic findings between fetuses with and without cystic fibrosis, except that one third-trimester fetus with cystic fibrosis had echogenic small bowel with shadowing. All of the fetuses with dilated bowel loops persisting at birth required surgery. Further studies are indicated to determine the exact risk of cystic fibrosis in this population.