Brittany is celtic, like Ireland and Wales where the incidence of neural tube defects is raised. We searched the hospital files in Brittany for all live and still births, and terminations of pregnancy after prenatal diagnosis for the years 1975-1984. 225 cases of spina bifida and 210 cases of anencephaly were identified; giving an incidence of 0.60 per 1000 births for spina bifida and 0.56 per 1000 births for anencephaly. No seasonality was found for both malformations. Analysis of the sex ratio for anencephaly indicated significantly higher proportion of females to males. Maternal age in the affected group was similar to the normal population. Casual heterogeneity among neural tube defects patients was presumed because 14% of our cases had other congenital anomalies.