More than 100 years after the first description of endometriosis, the pathophysiology of the disorder still remains an enigma. In addition to infertility, an increased frequency of clinically apparent spontaneous abortions (32% vs. 8-15% in the normal population and 19% in the infertile one) has been found in women with endometriosis and secondary infertility. Treatment of endometriosis with conservative surgery, danazol or both results in a frequency of spontaneous abortion within the range of the normal population's. Although the factors involved in the pathophysiology of endometriosis are probably multiple, abnormal corpus luteum function is a common mechanism that might explain both the infertility and the spontaneous abortions. Several studies suggested a relationship between endometriosis and corpus luteum function, which may be mediated by prostaglandins. However, not all the data have been supportive. We developed a hypothetical scheme (modified from Drake) that outlines possible mechanisms of endometriosis mediated by the adverse effects of increased prostaglandins. Further investigation of this scheme may provide new information about the pathophysiology of endometriosis.