Uterine fibroid. Light micrograph of a section through tissue from the uterus, in a case of a uterine fibroid (leiomyoma). A fibroid is a benign tumour of fibrous and muscular tissue, these tissues being found in the wall of the uterus. Most fibroids do not require treatment, but some can cause bleeding, pain and other disorders. Large fibroids may need to be surgically removed.