The incidence of spina bifida and anencephaly, according to reports, has declined in some parts of the world but not in others. It is suggested that social factors, greater awareness of the familial nature of these disorders coupled with the increased availability of effective contraception, may account for part of the decline and that these factors are less operative in the areas where no decline in incidence has been observed.

Data are presented for 65 families living in the Manchester area, each of which contained at least one affected child. Forty of these families appeared to have been ‘discontinued’ after the birth of the affected child.