Uterine polyps are growths attached to the inner wall of the uterus that extend into the uterine cavity. Overgrowth of cells in the lining of the uterus (endometrium) leads to the formation of uterine polyps, also known as endometrial polyps. These polyps are usually noncancerous (benign), although some can be cancerous or can eventually turn into cancer (precancerous polyps). Uterine polyps range in size from a few millimeters — no larger than a sesame seed — to several centimeters — golf-ball-size or larger. They attach to the uterine wall by a large base or a thin stalk. You can have one or many uterine polyps. They usually stay contained within your uterus, but occasionally, they slip down through the opening of the uterus (cervix) into your vagina.