BACKGROUND The risk of thromboembolic events related to the ethinyl estradiol (EE) dose in oral contraceptive (OC) pills has led to a further dose reduction. METHODS An OC pill with 150 micrograms desogestrel combined with only 20 micrograms EE was compared with a pill containing the same dose of desogestrel but 30 micrograms of EE in a Scandinavian multicentre study with follow-up visits after 3, 6 and 12 months. RESULTS In almost 5,000 cycles with each pill the numbers of pregnancies due to method failure with the lower and higher EE dose pills were 0 and 2, respectively. Irregular bleedings were slightly more common with the lower EE dose, but tended to decrease over the year of study. Other side effects were uncommon. Regarding metabolic effects, both pills tended to raise the plasma HDL level and the lower EE dose pill also reduced LDL. Free testosterone was reduced by two-thirds with both pills, showing beneficial effects on acne. CONCLUSIONS It is concluded that both these pills are reliable and safe, but that many women would accept a slightly greater risk of irregular bleeding with the 20 micrograms EE dose pill in exchange for a reduction in potential risk related to the estrogenic component of OC pills.