Extravillous trophoblasts are major participants in placental development and remodelling of spiral arteries. Trophoblast invasion is regulated by maternal immune cells, and abnormal leucocyte subpopulation composition has been reported in implantation failure. In pre-eclampsia (PE), with or without foetal growth restriction (FGR), superficial trophoblast invasion and insufficient remodelling of spiral arteries are common findings. In the present study, we have compared spiral artery remodelling and leucocyte composition in decidual tissue from 30 cases (PE=8, FGR=5, PE + FGR=17) and 31 controls. Six histological remodelling criteria were established, and each pregnancy obtained a remodelling score. Numbers of natural killer (NK) cells (CD56+), T cells (CD3+) and activated (CD25+ or CD69+) leucocytes were determined and related to total leucocyte (CD45+) numbers in serial sections. Cases demonstrated significantly impaired spiral artery remodelling, inappropriate placental growth and reduced NK cell proportions, as compared to controls (P=0.02, P<0.001 and P=0.01, respectively). Reduced NK cell proportion was primarily found in pregnancies complicated by FGR, with or without PE, and a significant positive correlation was observed between NK cell proportion, trophoblast infiltration and placental growth. Our in vivo observations support the hypothesized association between NK cells, impaired placental development and pathogenesis of PE/FGR.