We have studied 87 puerperal women during the first month postpartum. They were liable to ultrasound on the first, second and third day of this period. Eighteen of them were examined on the 15th and 30th day. The measure of the uterine area (pi x 1/2 length x 1/2 width) is seen as the most sensible method for this evaluation. The uterus involutionated symmetrically and in thirty days complete this process. They were no significative differences appreciated in the uterine involution that depends on the lactation, parity and the use of uterine retractors.