In the present article we examined the evidence of intrauterine device (IUD) insertion at different times during menstrual cycle with regard to bleeding, pain and ultrasound effectiveness. The study was performed on 100 patients with type TCu 380 IUD. The patients were further divided in 2 groups: the 1st group consisted of 50 of the patients (50%), in which the IUD was inserted on the 4th-6th day of the menstrual cycle, and the 2nd group, consisted on the other 50 patients (50%), in which the IUD was inserted in the 12th-14th day of the menstrual cycle. The following parameters were analyzed: bleeding during insertion, pain during insertion, pain after insertion, bleeding in the 1st week post-insertion, and ultrasound appearance after one week post-insertion. The results showed that the majority of women (72%) from the 1st group had a mean bleeding in comparison with the 2nd group in which most of the women (44%) had easily bleeding. Concerning the pain during assembly, it was showed that in the 1st group, the major of patients had mean pain (48%), comparing with the 2nd group in which the majority had mild pain (76%). Therefore, we sustain that the optimal period of IUD insertion could be the peri-ovulatory period, especially in patients who exclude the possibility of a pregnancy, until it is assembled. © 2018 Romanian Society of Ultrasonography in Obstetrics and Gynecology.