The incidence of neural tube defects among the siblings of 311 index cases has been estimated at 1.9%. The recurrence risk is higher for a same type malformation i.e. spina bifida after the birth of a child with spina bifida. The same features appear in other surveys from the literature although the general recurrence risk is lower in our series. The sex ratio appears to be inversely correlated with the incidence of the malformation, being higher in France than in Britain. Interpretation of the segregation analysis of the data is difficult. Genetic counseling is based upon the empirical risk (1.25% in the studied cases). Indications of antenatal diagnosis are discussed.