Endometriosis is the presence of endometrial tissue outside of the uterine cavity, most commonly surrounding the ovaries and fallopian tubes. It is a relatively common disorder in reproductive-age women and is associated with significant pain and morbidity. In most cases, the spread of extrauterine endometrial tissue appears t o result from retrograde menstruation and capillary or lymph dissemination. Endometrial cells implanted ectopically respond to cyclical changes in estrogen and progesterone with proliferation and secretion. Their presence in extrauterine areas can initiate immune and inflammatory responses that lead t o pain and peritoneal adhesions, and may interfere with fertility. Diagnosis is based on the occurrence of cyclical symptoms and surgical validation via laparoscopy or laparotomy. Treatment is aimed at alleviating pain and preventing complications. Most treatments work by reducing estrogen levels and/or menstrual cycling. A primary practitioner must understand not only the medical aspects of this disease, but the enormous social and psychologic costs as well.