Eleven cases of uterine lipomatous neometaplasia were studied. The patients ranged in age from 41 to 74 years (mean, 56.6 years). There were eight lipoleiomyomas and 3 angiolipoleiomyomas. In eight tumors the lipomatous component consisted only of mature lipocytes. In three tumors, pericapillary differentiating lipocytes also occurred. No correlation between the proportion of the lipomatous and leiomyomatous components and the size of tumor was observed. There was also no correlation between the amount and distribution of the lipomatous component and the hyalinized fibrous stroma. The levels of cytosolic estrogen and progesterone receptors, studied in one case, were lower in the lipoleiomyoma than in the myometrium. Leiomyomas and adenomyosis were the most frequent accompanying lesions. The study supports a notion that uterine lipomatous neometaplasia originates from pericapillary pluripotential mesenchymal cells. Present findings suggest that lipomatous differentiation of immature neoplastic cells can occur in a preexisting leiomyoma, as well as simultaneously with leiomyomatous differentiation.