It is becoming increasingly apparent that mild or moderate hyperhomocysteinaemia may be associated with adverse perinatal complications and outcomes. The placental pathology in 14 pregnancies from 11 women diagnosed retrospectively to have hyperhomocysteinaemia, following a recent history of intrauterine fetal growth restriction, abruption or of thromboembolic disease, were reviewed. Most of the placental findings indicated abnormal placentation but these were not specific to maternal hyperhomocysteinaemia nor found in every placenta. Features observed included absence of trophoblast-induced physiological vascular changes, acute atherosis, intraluminal endovascular trophoblast in the third trimester, infarction, retroplacental haematoma formation and accelerated villous maturity. Uteroplacental vascular thrombosis was also seen. Three of the women had a subsequent pregnancy where they were treated empirically with folic acid, and these resulted in improved perinatal outcomes. The finding of placental pathology warrants investigation of the woman for hyper- homocysteinaemia. Further randomised controlled trials of folic acid supplementation in preventing pregnancy complications associated with hyperhomocysteinaemia should be conducted.