The presence of fatty tissue in the myometrium is anomalous; this alteration has been interpreted either as a lipomatous degeneration or as a metaplasia of smooth muscle cells or, still, as a real neoplasm, frequently associated with a leiomyoma, the so-called lipoleiomyoma. The observation of a case of lipoleiomyoma stimulated us to ascertain the real incidence of this lesion which is commonly considered to be rare. We examined 620 single or multiple uterine leiomyomas with extensive sampling of all the areas suspected to contain fatty tissue islands. Five times out of seven the presence of fat cells in a leiomyoma resulted to be a true lipoleiomyoma. It has thus been possible to ascertain the incidence of lipoleiomyoma versus uterine leiomyomatosis (0,8%). Futhermore we observed a prevalence in menopause, an association with multiple leiomyoma and a preferential onset in the subserosa. The pathogenesis of this lesion, which can be fully ascribed to a mixed, benign, heterologous, mesenchymal neoplasm, is briefly discussed.