Background and Objective. It is unclear how immune tolerance develops to a semiallograft fetus in pregnancy. Human leukocyte antigen G (HLA-G) expressed by extravascular trophoblasts plays an important role in the recognition of the gestational tissues as self and the development of immune tolerance against the gestational tissues by the maternal immune system. The soluble form of the HLA-G (sHLA-G) molecule in the maternal serum is also reported to contribute to the prevention of rejection during pregnancy. The aim of the study was to compare the maternal serum sHLA-G levels of the women with missed abortions and control subjects with uncomplicated pregnancies.