To get information about embryologic mechanisms of neural tube defects (NTD), by studying the associated malformations. Eighty three cases of NTD, seen at the prenatal diagnosis unit of Rennes University Hospital (France) between May 1999 and December 2002, were retrospectively studied. Cases with chromosomal anomalies (5/83), cases without available karyotype or pathologic examination were excluded. 24 spina bifida, and 27 cephalic forms (anencephalies, exencephalies, and encephaloceles) were thus analyzed. Only 22/51 cases (43%) were strictly isolated NTD. Anomalies of tissues arising from neural crests were noted in 8/51 fetuses (16%), midline or lateralization anomalies in 12/51 (24%), and anomalies of mesoblastic tissues in 17/51 (33%). An already known syndrome was found in 4/51 cases (8%). NDT are more extensive congenital damages that would suggest the restrictive terminology. That prompts to assess cautiously prenatal diagnosis of NTD, and to get detailed pathological examination after termination of pregnancy. Copyright (c) 2007 John Wiley & Sons, Ltd.