Abnormalities of the L1CAM gene, a member of the immunoglobulin gene superfamily of neural-cell adhesion molecules, are associated with X-linked hydrocephalus and some allelic disorders. Hirschsprung's disease (HSCR) is characterized by the absence of ganglion cells and the presence of hypertrophic nerve trunks in the distal bowel. There have been three reports of patients with X-linked hydrocephalus and HSCR with a mutation in the L1CAM gene. We report three more patients with similar conditions. We suspect that decreased L1CAM may be a modifying factor in the development of HSCR.