The objective of the study was to investigate histological changes in the endometrium in 20 volunteers treated with a low-dose, gestodene-containing triphasic oral contraceptive. Endometrial biopsy specimens were taken before, during a 6-month period of oral contraceptive use and in a post-treatment period. These specimens were evaluated using light microscopy, scanning and transmission electron microscopy. In addition, ultrasound examinations of the uterus, endometrial thickness and ovaries were performed. The low-dose, gestodene-containing triphasic oral contraceptive had no adverse effects on the endometrium (e.g. no proliferation, no polyps, no inflammatory processes), was well tolerated and showed a low side-effect profile. The inhibition of endometrial transformation was demonstrated both by endometrial morphology as well as by endometrial thickness, as measured by transvaginal ultrasound examination.