There is evidence that women with a high body mass index may have a higher risk of miscarriage. It is not known if this is due to an endometrial or embryo defect. The aim of this retrospective study was to examine markers of endometrial function in overweight and obese women with recurrent unexplained miscarriage. A total of 136 women were included in the study and classified according to their body mass index (BMI) into two groups, normal BMI (< 25 kg/m(2), n = 70) and high BMI (> or = 25 kg/m(2), n = 66). Endometrial morphology was examined in all patients. A subgroup of 28 patients was examined for endometrial oestrogen and progesterone receptors in different components of the endometrium, and in a further subgroup of 28 patients, endometrial glandular leukaemia inhibitory factor and leukocyte populations were examined. A modest increase in the BMI (30.4 +/- 0.71 kg/m(2)) does not have a significant impact on endometrial steroid receptors, leukocyte populations or endometrial morphology. However, there was a significant negative correlation between endometrial glandular leukaemia inhibitory factor concentrations and the BMI (r = -0.4, P = 0.02), warranting further investigation in prospective studies that include patients with higher BMI levels.