The authors monitored the involution of the uterus during the first month after childbirth by means of clinical examinations and abdominal ultrasound. 156 clinical and ultrasound examinations were performed in 77 women on D2, D7 and D28. The size of the uterus and the uterine cavity were measured on the longitudinal sections only. The other incidences, and particularly the axial incidence, made it possible to describe the aspects of the uterine cavity. Uterine involution is rapid during the first week and then slows down. By D28, the dimensions of the uterus have returned to the upper limit for the non-pregnant uterus. During the first week the emptiness line is visible in one out of 13 cases. Hematometra is visible in one out of 6 cases and more frequent on D7 than on D2. It gave rise to no clinical signs. In all cases, an emptiness line was observed on day 28 postpartum.