The paper analyzes the results of recent studies of the major clinical and morphological types of simple and proliferating uterine myoma. The etiology and pathogenesis of the two types of myomas are compared using the results of cytogenetic (loss of heterozygosity and microsatellite instability at chromosomal sites), molecular genetic, endocrinological, and immunological studies and investigations of intercellular interaction. Issues in the differential diagnosis of proliferating uterine myoma and leiomyosarcoma are considered.