A 24-year-old female with infected urachal cyst is reported. She was admitted to the hospital with complaints of a lower abdominal mass, abdominal pain and cystitis symptom. Brownish pus discharges from her umbilicus were recognized by manual compression of the lower abdominal mass. Cystoscopy revealed a small orifice at the dome of the bladder, and pus discharges from this orifice. A pooling of contrast medium (8 X 2.5 cm) under the umbilicus was detected by a fistelography from the umbilicus, and a low density mass was detected under the abdominal wall between the umbilicus and the dome of bladder on a CT scan. So she was diagnosed as an infected urachal cyst and operated on. The urachal cyst which was adhered to the peritoneum had penetrated both the umbilicus and bladder at the time of operation. Complete removal of the urachal cyst with partial cystectomy was done. We also reviewed the Japanese case reports of urachal cyst.