Endometriosis is a condition in which the endometrium, the layer of tissue that normally covers the inside of the uterus, grows outside of it. Most often this is on the ovaries, fallopian tubes, and tissue around the uterus and ovaries; however, in rare cases it may also occur in other parts of the body. The main symptoms are pelvic pain and infertility. Nearly half of those affected have chronic pelvic pain, while in 70% pain occurs during menstruation. Pain during sexual intercourse is also common. Infertility occurs in up to half of women affected. Less common symptoms include urinary or bowel symptoms. About 25% of women have no symptoms. Endometriosis can have both social and psychological effects.