Benign mesenchymal tumours of the uterus are discussed. The results are compared with those of other authors and respective epidemiological findings are put forward. Clinical and histological characteristics of uterine myomas and adenomyomas are described in more detail. Irregular bleeding is most frequent among clinical symptoms; it is caused by the persistence of the proliferative endometrium. The secretory conversion of the ectopic endometrium in adenomyoma appears in the glandular epithelium only, while the stromal response to progesteron activity seems inadequate. Maturation of the ectopic and the uterine endometrium is discordant. The cause is the retardation of both the proliferative and secretory phases in the ectopic endometrium. After secretory conversion of the ectopic endometrium the exhaustion and destruction of glands appears. The regeneration of the ectopic endometrium fails to occur because of the absence of the basal layer in the ectopic endometrium. Therefore the authors suppose that the regression of the ectopic endometrium in adenomyomas might be the result of ovulatory cycles.