Smooth-muscle tumors of uterine origin encompass a broad family of neoplasms. The leiomyoma, by far the most common of all the neoplasms, generally is hormone sensitive, with rates of growth semiquantitatively related to estrogen and progesterone receptor levels. Several forms of degenerative change can occur in the leiomyoma. The most common is hyaline degeneration, which is important in that it should not be mistaken for the coagulative tumor cell necrosis seen in leiomyosarcoma. Red degeneration (necrobiosis) is a form of degeneration that occurs characteristically but not exclusively in pregnancy, and the process is often the cause of pain and fever. Several forms of treatment have been used medically in the treatment of leiomyoma. Gonadotropin-releasing hormone analogs or agonists or selective arterial embolization with polyvinylformaldehyde particles may lead to substantial degeneration or infarction of the leiomyoma, respectively. Several variants of leiomyoma, the cellular and symplastic leiomyomas, are important to recognize, as they can be misinterpreted as sarcoma. In addition, there are two unusual growth patterns of leiomyoma that are important to recognize. Both the benign metastasizing leiomyoma and disseminated peritoneal leiomyomatosis are found outside the uterus, and neither is malignant. Recent studies offer insights into their origin and hormonal influences. From a diagnostic and therapeutic point of view, the leiomyosarcoma, while rare, is clinically of great import. Coagulative necrosis, cytologic atypia, and mitotic counts are all important in diagnosing the condition.