We report forty cases of congenital autosomal fragile sites, which have been analysed genetically and cytogenetically in the light of previous reports in the literature. The nature of the lesion of DNA at the fragile site is unknown. In contrast with the fragile site Xq27 there is no particular phenotype associated with autosomal fragile sites. The incidence of early spontaneous abortion and of chromosomal abnormalities in the offspring of carriers of these inherited autosomal fragile sites suggests the possibility of prenatal diagnosis.