Ganglioneuromatosis of the gastrointestinal tract is a rare condition that has an established association with the multiple endocrine neoplasia syndrome, type IIb. Its occurrence in neurofibromatosis, in which the large intestine is usually affected, is much rarer. We report a case of diffuse ganglioneuromatosis of the small bowel, found incidentally during surgery for a malignant peripheral nerve sheath tumor arising in the retroperitoneum in a 32-year-old man with neurofibromatosis type 1, and review previously reported cases.