INTRODUCTION: Recurrent pregnancy loss (RPL) of unknown etiology is correlated with immunological alterations during pregnancy. Normally, changes in leukocyte subpopulations and HLA expression take place in pregnant uterus in order to tolerate the semi-allogenic embryo.OBJECTIVE: Our research tries to enlighten the immunological changes that take place in the uterus of women with recurrent abortions of unknown etiology during first trimester of pregnancy.MATERIALS AND METHODS: The miscarriage group was obtained from 25 women who miscarried between the ages of 35 to 42 years and controls consisted of 25 healthy women between the ages of 27 to 39 years, who had electively terminated their pregnancies during the first trimester of pregnancy. The abortion was processed and specimens taken were studied using immunohistochemical methods. Specimens were taken from decidua basalis and decidua parietalis. Monoclonal antibodies were used against HLAG (Human Leukocyte Antigen G), CD68( Cluster of Differentiation 68), CD56, CD16 and CD25. The results were statistically analysed with Mann-Whitney test.RESULTS: HLA-G expression in decidua basalis from miscarriage group was found to be decreased. CD25+ cell expression was found to be invariable in deciduas from both groups. CD16+ cell and CD68 + cell expression was found to be increased in deciduas from the miscarriage group. CD56+ cell expression was found to be increased in decidua parietalis from miscarriage group. Conclusion : Several differences in the immunological profile of deciduas from RPL group were observed. Changes in feto-protective HLA-G expression and a possible implication of macrophages and NK cells were found.