In order to assess whether markers of cell senescence are related to reproductive failure, the expression of telomerase and telomere length in endometrial biopsies from women with and without reproductive failure were assessed. This pilot study included 45 women of whom 10 had idiopathic recurrent loss of empty gestational sacs, 10 had idiopathic recurrent fetal loss (miscarriage following identification of fetal cardiac activity), 10 had recurrent implantation failure and 15 had two or more normal pregnancies (control group). An endometrial sample was collected during the window of implantation from each woman. The mean endometrial telomere length was determined by quantitative polymerase chain reaction. Telomerase expression was evaluated by immunohistochemistry. The endometria of the control group showed virtually no telomerase immunoreactivity during the window of implantation. However, the immunostaining for telomerase was significantly and differentially increased in various endometrial cellular compartments in women with recurrent reproductive failure (P < 0.05). There were no significant differences in mean telomere length between groups. These data provide a novel insight into the biological correlates of clinical types of recurrent reproductive failure and suggest that specific alterations in the regulation of endometrial cell fate are associated with different types of recurrent reproductive failure.