Progressively increasing menstrual cramping may be a symptom of endometriosis. These are caused by contractions of uterine muscle initiated by prostaglandins released from the endometrial tissue. A puzzling feature of endometriosis is that the degree of pain it causes is not related to the extent of the disease. Some women with extensive disease feel no pain at all. A woman with endometriosis may notice that as the disease progresses her periods become more painful or that the pain begins earlier or lasts longer.