In pregnant women with severe von Willebrand's disease, the prepartum period should include monitoring for a rise in factor VIII-related activities (factor VIII coagulant activity [factor VIII:C], factor VIII-related antigen [VIII R:Ag], and factor VIII ristocetin cofactor [factor VIII R:Cof]). Two women whose pregnancies were so monitored were delivered of normal infants: one by cesarean section and one by vaginal delivery. The failure of factor VIII:Ag or factor VIII R:Cof to rise above the level of 50% at term in the woman who delivered vaginally predicted hemostatic difficulty during the postpartum period. She was, therefore, treated with cryoprecipitate. In the woman who gave birth by cesarean section, although all factor VIII-related activities rose into the normal range, the additional surgical trauma anticipated in cesarean section prompted the use of cryoprecipitate as well.