Diffuse uterine leiomyomatosis (DUL) is a rare entity with an unknown etiopathogenesis. A 24 years old female presented with abdominal discomfort and menorrhagia. Clinical and ultrasonographic examination revealed an enlarged uterus. The hysterectomy specimen showed a symmetrically enlarged uterus with a bosselated external surface. The cut surface showed multiple nodules of varying sizes diffusely involving the myometrium. Microscopically, the nodules were leiomyomas of varying degrees of cellularity. Some of the leiomyomas showed an increased vascularity either in the form of congeries of blood vessels with a lobular arrangement or occasionally as foci of 2-3 vessels. The vessels were surrounded by whorls of spindle cells. On immunohistochemistry the leiomyomas expressed vimentin, smooth muscle actin (SMA), desmin and CD10: the cells whorling around the blood vessels expressed vimentin, SMA and focally desmin and were negative for CD10 and HMB-45. The aim of this paper is to document that CD10 is expressed in diffuse uterine leiomyomatosis and discuss the histogenesis of DUL.