The nuclear factor kappa B is widely expressed in the distinct subpopulations of chorionic villi and deciduas of first-trimester pregnancies. We examined the cellular distribution and expression of nuclear factor kappa B in the human first-trimester chorionic villi and deciduas of women with early spontaneous miscarriage and viable pregnancy by confocal laser scanning microscope and immunohistochemistry. There is a greater nuclear translocation of nuclear factor kappa B is restricted to villous stromal cells, decidual stromal cells, glandular epithelial cells and vessel endothelial cells in early spontaneous miscarriage than in viable pregnancies. Collectively these observations suggest that over-activation of nuclear factor kappa B has a relationship with early spontaneous miscarriages.