Recent research on the pathogenesis of endometriosis has provided more evidence that factors in peritoneal fluid (PF) may play a role in the progression of the disease. Examples of these factors are mterleukin (IL)-8. RANTES (regulated on activation, normal T cell expressed and secreted), IL-13, IL-10, and monocyte chemoattractant protein-1. These factors are associated with proliferation of endometrial cells, changes in the cytotoxicity of peritoneal macrophages, and the responsiveness of ectopic endometrium to cytolysis. Differences in the characteristics of the ectopic and eutopic endometnum, eg, aromatase expression, matrix metalloproteinases, apoptosis markers, and integrin expression have also been shown. The effect of endometriosis on reproductive outcome as well as its pathophysiologic mechanisms have been investigated. Treatment options for endometriosis-associated infertility or pelvic pain that give maximal pain relief and fertility outcome with fewer side effects have been evaluated. Resection or ablation of even minimal or mild lesions is now recommended for the treatment of endometnosis-associated infertility.