The identification of carriers and the prenatal diagnosis of hemophilia A have greatly improved with knowledge of the structure of the factor VIII gene. This has permitted the defect to be traced in families by using restriction fragment length polymorphisms. This study summarizes 5 years' experience at A. Bianchi Bonomi Hemophilia and Thrombosis Center and the problems encountered. One hundred and forty-four women at risk of hemophilia A from 93 families were referred to our center for DNA analysis. Carrier detection was performed in 95 women, including 11 who were pregnant. Prenatal diagnosis was performed at 7-14 weeks' gestation in 56 pregnant women. We employed two intragenic restriction fragment length polymorphisms (XbaI and BclI) and the two extragenic restriction fragment length polymorphisms (TaqI and BglII). Combining the results of intra and extragenic restriction fragment length polymorphisms with pedigree analysis, a diagnosis was reached in approximately 90% of cases. Of the 33 male fetuses, 11 were affected and 19 not affected. Two cases of recombination between extragenic restriction fragment length polymorphisms and the factor VIII locus were found.