 Tibolones effects on the endometrium have been studied by a number of investigators 8-14 using transvaginal ultrasound TVUS and histology in biopsies after long-term treatment. With ultrasound it was observed that after 6 years of treatment endometrial thickness was slightly increased p 0.05, 8 in tibolone-users compared to controls. Dőren et al. 9 confirmed that tibolone treatment results in a slight increase in endometrial thickness, which was not different from estrogen norethisterone acetate treatment E2NETA. Histology data after tibolone use for more than 3 months, show no change in 90 of the subjects and only in a few cases an endometrial profile was shown which was comparable to the early follicular phase of a normal cycle 15. Even after two years of tibolone use hyperplasia rarely occurs 10. 