The placental lesion of fetal artery thromboses is characterized by collapse and obliteration of chorionic vasculature, an increase in stromal connective tissue and syncytial knots, with a thickening of trophoblast basement membrane. An additional feature, not previously described in association with the lesion, is linear trophoblast basement membrane haemosiderosis. Thirty-five such lesions were examined for this feature which was identified in 32. Random tissue sections of placentae from cases of intrauterine death showed a similar basement membrane haemosiderosis and were used as positive controls. None of 20 normal control cases examined demonstrated the feature. Electron microscopy demonstrated electrondense bodies within the basement membrane. Spectrographic analyses confirmed the presence of iron within these deposits. The significance of this finding lies not so much in the fact that it is an additional finding in fetal artery thrombosis but rather in the underlying pathophysiology.