Fibroids most commonly develop in the uterus, but in rare cases they may affect other organs. Fibroids begin in smooth muscle cells, usually in the uterus. However, they may develop in other areas where smooth muscle cells are found. Rarely, a fibroid may invade other nearby organs. These types of fibroids, called parasitic fibroids, develop on a "stalk" coming from the uterus and eventually travel and attach themselves to the other organs, where they can cause serious complications.