Endometriosis is an estrogen-dependent, progesterone-resistant disorder largely derived from retrograde transplantation of menstrual tissue/cells into the pelvis, eliciting an inflammatory response, pelvic pain, and infertility. Eutopic endometrium (within the uterus), giving rise to pelvic disease, displays cycle-dependent transcriptomic, proteomic, and signaling abnormalities, and although its DNA methylation profiles dynamically change across the cycle in healthy women, studies in endometriosis are limited. Herein, we investigated the DNA methylome and associated gene expression in three phases of the cycle in eutopic endometrium of women with severe endometriosis versus controls, matched for ethnicity, medications, smoking, and no recent contraceptive steroid use. Genome-wide DNA methylation and gene expression were coassessed in each sample. Cycle phase was determined by histology, serum hormone levels, and unsupervised principal component and hierarchical cluster analyses of microarray data. Altered endometrial DNA methylation in endometriosis was most prominent in the midsecretory phase (peak progesterone), with disruption of the normal pattern of cycle-dependent DNA methylation changes, including a bias toward methylation of CpG islands, suggesting wide-range abnormalities of the chromatin remodeling machinery in endometriosis. DNA methylation changes were associated with altered gene expression relevant to endometrial function/dysfunction, including cell proliferation, inflammation/immune response, angiogenesis, and steroid hormone response. The data provide insight into epigenetic reprogramming and steroid hormone actions in endometrium contributing to the pathogenesis and pathophysiology of endometriosis.