Eighty-two patients treated surgically for myelomeningocele or myelodysplasia between 1945 and 1993 are presented. Family and environmental history has been studied. The presence of genetic markers (HLA B27, ABO, Rh) has been investigated. Heterogenicity of localization and type of defect in the series reviewed has been found. Associations between certain genetic features confirm multisite mechanism of closure of the neural tube. The relationship between site of neural tube defect and concurrence of developmental defects has been substantiated. A higher site often results in multiple defects.