The aim of our study was to examine the effects of hormone replacement on the size of the uterus and the development or increase of myomatas. Fifty perimenopausal women were included in the study (53.8 +/- 5.0 years). Patients received a substitution therapy composed of a combination of 4 mg estradiovalerate and 200 mg prasteronenantate (Gynodian Depot cartridges) given as a muscular injection in 6-10 week intervals (mean 7 weeks +/- 4 days). Prior to the onset of therapy with Gynodian and after a period of 12 months (+/- 13 days) vaginosonography was performed. Measurements taken were length, thickness, height of endometrium, size of ovaries and of myomas. Data obtained were correlated with baseline findings. Within 1 year, significant increases in uterus length from 73.4 mm to 88.2 mm, in uterus thickness from 33.9 mm to 43.5 mm and in endometrium height from 4.1 mm to 6.7 mm were observed (median values). There was an increase in both the number (from 2.2 to 3.5) and the size of the myomatas (29.4-35.0 mm diameter). A statistical analysis conducted by means of the Wilcoxon matched pairs signed-rank sum test showed P < 0.001. No significant change occurred in the size of the ovaries. Our study shows that hormone substitution may have an impact on uterus growth and that therefore vaginosonographical monitoring can be recommended.