Subinvolution of placental bed vessels, a well-recognized cause of postpartum and postabortal hemorrhage, is defined with prolonged or excessive uterine hemorrhage beginning after the delivery or abortion. Although physiological changes in uteroplacental parts of spiral arteries are well known, the sequence of events in involution of these vessels is not yet clearly understood. In this article we present two cases of subinvolution of placental bed vessels in which we were able to demonstrate the presence of extravillous trophoblast in and around the placental bed vessels. The disease is supposed to be the result of abnormal interaction between maternal uterine cells and fetal trophoblast.