The authors present a review of 431 children biopsied and studied with the following histochemical and immunohistochemical techniques: 1) acetylcholinesterase activity; 2) alphanaphthylesterase activity; 3) S-100 protein immunohistochemical technique; 4) glyoxylic acid method. Two hundred forty-eight patients of our series presented different forms of dysganglionosis, 12 of them (4.8%) presenting neuronal intestinal dysplasia type B. In 7 cases, NID type B was diffuse, whereas in 5 recto-colonic NID type B was confined to the splenic flexure. Male:female ratio was 9:3. Familial recurrence was present in 2 of the 12 cases of our series, affected by severe neuronal intestinal dysplasia extended to the small intestine, associated with intestinal malrotation and short bowel syndrome. Four of the 7 cases of diffuse NID type B and 2 of the 5 cases of rectocolonic NID type B were surgically treated. Three patients with diffuse NID died from sepsis within the 2nd year of life. This study confirms that NID type B is a form of dysganglionosis which can be diagnosed in a Mediterranean country if histochemical techniques are applied in the study of a large series of constipated and pseudo-Hirschsprung patients. From a pathogenetic point of view, the authors compared the histochemical findings of biopsies from their series of NID patients with those of recto-colonic biopsies from patients with MEN II B syndrome. The similarity of GI symptoms in MEN II B and NID pediatric patients suggests that the two disorders could be the result of mutations affecting the same domain of the RET proto-oncogene.