Uterine polyps are growths that adhere to the inner uterine wall and extend into the uterine cavity. The excessive growth of cells in the uterine lining (endometrium) leads to the formation of uterine polyps, also called endometrial polyps. These polyps are generally not cancerous (benign), although some may be cancerous or may develop into cancer (precancerous polyps). The size of the uterine polyps varies from a few millimeters, not bigger than sesame, to several centimeters, the size of a golf ball or more. They attach to the uterine wall with a large base or a thin shaft. You can have one or more uterine polyps. They usually remain trapped in your uterus, but sometimes slide through the opening of the uterus (cervix) into your vagina. Uterine polyps are more common in postmenopausal women, although younger women may also be affected.