Four hundred ninety-eight acetylcholinesterase-stained suction rectal biopsies from 456 children were examined to assess the occurrence of "isolated" or "primary" intestinal neuronal dysplasia at Children's Hospital of Pittsburgh. Cases of proven Hirschsprung's disease were excluded. In 38 biopsies from 38 patients, we found a mild to moderate increase in mucosal acetylcholinesterase staining and abundant submucosal ganglion cells (large, irregular ganglia or at least five ganglia per HPF). This group was clinically heterogeneous with a frequent history of prematurity and small left colon/meconium plug syndrome, protein/formula intolerance, or obstructive anatomic gastrointestinal abnormalities. We feel that isolated "intestinal neuronal dysplasia," as diagnosed by suction rectal biopsy and the above criteria, is a descriptive biopsy appearance. Rather than characterizing a unique disease entity, it is encountered in a variety of clinical situations. Based on our observations and review of the literature, we therefore conclude that "intestinal neuronal dysplasia" not associated with Hirschsprung's disease, neurofibromatosis, or multiple endocrine neoplasia syndrome has yet to be well defined in clinical and histopathologic terms. The histologic diagnosis, at this time, should be reserved for those rare, florid cases of parasympathetic hyperganglionosis that are documented by adequate tissue sampling.