Tamoxifen used for adjuvant therapy in breast cancer, has a complex and unclear action on endometrium and myometrium. Many authors demonstrated endometrial proliferous changes in peri and post menopausal women. Our study shows the development of myomas in three patients without uterine pathology before tamoxifen therapy, and the increase of a polip and a myoma after tamoxifen therapy. Moreover, we observed the development of a myoma in a patient after one year tamoxifen in association with LH-RH analogue therapy. It is necessary to continue our study with a larger number of patients to assess the hyperplasic effect of tamoxifen.