The paralysis associated with lumbosacral meningomyelocele has been attributed both to myelodysplasia and to degeneration of the exposed neural tissue. Surgically created dysraphism shows that exposure of an intact spinal cord in a genetically normal animal results in degeneration of the normal nervous tissue and subsequent paralysis. Our objective was to study neuronal differentiation in the curly tail mouse mutant model, which develops lumbosacral meningomyelocele naturally and is a phenocopy of nonsyndromic human neural tube defects. Prenatal repair of meningomyelocele assumes that the normal neuronal differentiation program occurs despite failure of neurulation. Here we demonstrate that this most suitable animal model has normal differentiation of neuronal structures at the level of the meningomyelocele. TuJ1, an antibody to neuronal specific class III beta-tubulin, an early marker of neuronal differentiation, was used to stain paraffin-embedded sections of curly tail mouse embryo meningomyelocele. Embryos were examined at embryonic day 13.5 (E13.5). The inbred mouse strain, C57BL6/J, which is genetically similar to the curly tail mouse, was used as a control in these studies. We show that early neuronal differentiation appears intact within the meningomyelocele. TuJ stains structures within the open neural tube. Motor neurons are present in the ventral horn and ventral roots. Dorsal root ganglia are present and of similar size to controls. The staining pattern is similar to that seen in the C57BL/6J control mouse, although dorsal structures are laterally displaced in the curly tail meningomyelocele. Based on this model, fetal surgery to repair human meningomyelocele may preserve neurological function in those cases where there is not an inherent genetic defect of the neural tissue.