The urachal cyst is a rare congenital anomaly due to a lack of apposition of sheets remains allantoid. Diagnosis is based on prenatal ultrasound. We report the case of an urachal cyst diagnosed in a female fetus in the third trimester of pregnancy which regressed spontaneously in the postnatal period. Comment: Mrs. CD, a 27 year-old consulted us as part of the regular monitoring of a normal course of pregnancy. At 32 weeks, ultrasounds showed an anechoic oval-shaped and well-limited image located above the upper pole of the bladder, below the insertion of the cord. Diameter was 12 mm and the image was connected to the baldder through a thin orifice. The umbilical ring appeared wide and connected to the abdominal collection by a 5 mm-channel. However, the skin surface was normal with no solution of continuity. On ultrasound at 37 weeks gestation (WG), the pelvic anechoic image kept the same features but the thin connection was no more visible. Vaginal delivery occurred at 40 GW and 5 days. Examination of the newborn found normal abdominal skin covering. By 12 months, ultrasounds found that the cyst completely disappeared. Conclusion: The permeable urachus is a progressive disease. Its development depends on the clinical form of its manifestation. Surgical treatment is often necessary, but spontaneous regression is possible for simple cysts until postnatal period.