['To evaluate p27 protein expression in the endometrium of women with endometriosis.', 'Transversal case-control study.', 'Endometriosis Unit, Federal University of São Paulo, Brazil.', 'Thirteen patients with stage I/II endometriosis, five with stage III/IV endometriosis, and 11 control subjects.', 'Endometrial biopsies were obtained from patients with proven endometriosis and women without disease at laparoscopy. P27 protein was immunolocalized in the biopsy tissues and quantified by light microscopy.', 'Immunostaining scores of glandular and stromal cells in endometrial biopsies obtained from patients with confirmed endometriosis compared with those of healthy control women with normal pelvis at laparoscopy. The staining scores of stage I/II and stage III/IV patients and of both patient groups and the control group were compared.', 'The level of p27 protein expression observed in the control group, both in the stroma and in the endometrial glands, was significantly different from that observed in the endometriosis patient groups. Significant differences in p27 protein expression levels in the glandular epithelium and stroma were not observed among groups of patients with endometriosis.'] Is p27Kip1 down-regulated in the endometrium of women with endometriosis?