A disease of the female reproductive system in which cells similar to those in the endometrium, the layer of tissue that normally covers the inside of the uterus (i.e., the inner lining of the womb), grow outside the uterus. Lesions can be found on ovaries, fallopian tubes, tissue around the uterus and ovaries (peritoneum), intestines, bladder, and diaphragm; it may also occur in other parts of the body.