OBJECTIVE: To present prenatal ultrasound findings and molecular diagnosis of microvillus inclusion disease, and to review the literature of abnormal prenatal ultrasound findings associated with congenital diarrhea. MATERIALS, METHODS AND RESULTS: A 21-year-old woman, gravida 1, para 0, had generalized bowel dilation of the fetus on prenatal ultrasound at 29 gestational weeks. She and her husband were non-consanguineous, and there was no family history of congenital diarrhea. Prenatal ultrasound at 29 gestational weeks revealed a honeycomb appearance of the bowel without ascites or intraperitoneal calcification. At 36 gestational weeks, polyhydramnios dilated bowel loops were observed, and a 3,355-g male baby was delivered with a distended abdomen. Postnatally, the neonate suffered from watery diarrhea and abdominal distension but there was no mechanical bowel obstruction. An endoscopic biopsy of the small bowel revealed intracytoplasmic inclusions lined by intact microvilli in the apical surface of the intestinal epithelial cells consistent with the diagnosis of microvillus inclusion disease. Mutation analysis of blood samples of the neonate and parents revealed a heterozygous nonsense mutation of c.445C <T, p.Q149X in exon 4 of the MYO5B gene in the father and proband, and a heterozygous nonsense mutation of c.1021C < T, p.Q341X in exon 9 of the MYO5B gene in the mother and proband. CONCLUSION: Prenatal sonographic identification of dilated bowel loops in association with polyhydramnios suggests congenital diarrhea and a differential diagnosis of microvillus inclusion disease in addition to congenital chloride diarrhea and congenital sodium diarrhea. Molecular analysis of the MYO5B gene is helpful in genetic counseling and prenatal diagnosis of recurrent microvillus inclusion disease in subsequent pregnancies.