The objective of this study was to observe the position dynamics of the T-shaped intrauterine device (IUD) in the uterine cavity, from insertion to 90 days of use. IUD position was evaluated in 214 women by vaginal ultrasound, measuring the IUD-endometrium, IUD-myometrium, and IUD-fundus distances. The 90th percentile of the IUD-endometrium distance was 5, 6, and 8 mm at time of insertion, 30 and 90 days of use; 7, 9, and 10 mm for IUD-myometrium distance; and 23, 24, and 27 mm for IUD-fundus distance, respectively. Seventeen IUDs were classified as misplaced at insertion by using the 90th percentile of the IUD-myometrium distance as standard. Of these, only 6 remained misplaced after 90 days of use. On the other hand, 21 IUDs were beyond the 90th percentile at the 90-day observation, only 6 of which were considered misplaced at insertion. We conclude that the T-shaped IUD accommodates its position in the uterine cavity during the first 3 months following insertion, and that ultrasound evaluation of its position is not a good predictor of future evaluation.