Summary Background: The aim of the study was a histologic evaluation of placentas and chorions from pregnancies complicated by antiphospholipid syndrome (APS) and inherited thrombophilia in women treated with anticoagulants and in a group of women without the anticoagulant treatment. Material: 24 placentas from 18 patients with acquired and inherited thrombophilia and 23 chorions from 19 miscarriages in women with the same diagnosis were included in the study. There were 33 chorions from miscarriages from healthy women and 25 placentas from uneventful pregnancies in the control group. Biopsies from placentas and chorions were stained with eosin and hematoxylin and evaluated for the presence of villous thrombosis, fibrin deposits, intraplacental hematomas, thrombosis in fetal circulation and other histological findings. Results: In the placentas from pregnancies complicated with APS and inherited thrombophilia, the presence of fibrin deposits in the basal and villous plate, stasis in the fetal circulation and thrombosis in the villous plate and villous vessels, were statistically more frequent (p<0,001) comparing with physiological pregnancies. In the material from miscarriages the presence of fibrin deposits was statistically more common (p<0,001) in women with thrombophilia. The number of physiological findings in placentas of women treated with anticoagulants in pregnancy and in the non-treated ones, whose pregnancies resulted in fetal demise, were not statistically different. Conclusions: 1. Fibrin deposits between villi and villous plate are the most recognizable features in placentas and chorions from APS pregnancies 2. In women with APS impaired trophoblast invasion seems to be the most likely cause of recurrent miscarriages 3. Anticoagulant therapy does not prevent either fibrin deposits collection or other placental changes