170 nulliparous women were inserted with the mini MLcu 250 IUD, a device smaller than the rest; they were observed for 831 cycles. Most women were above 26 years of age, and 66% had experienced either spontaneous or induced abortion, or extrauterine pregnancy. 75% chose the pill for personal convenience, and 25% because they could not take OC (oral contraception). There were 4 pregnancies, i.e. a Pearl index of 5.7. There were 17 expulsions and 6 removals of the IUD, i.e. a continuity rate of 61%. It is concluded that the idea of nulliparous women having a smaller uterine cavity is totally erroneous, and that hysterometry gives only an approximate measure of it. Echography will be able, in the near future, to provide gynecologists with a more exact knowledge of the dimensions of the uterine cavity, thus bringing about a better choice of IUD for the single patient, and better continuation rates for all types of IUDs.