Although most cases of urachal cyst are asymptomatic, they are frequently detected after complication by infection. We report a 43-year-old woman who was diagnosed preoperatively an infected urachal cyst and was performed primary excision. A pus culture drained from the cyst was no growth in microscopic exam. Pathologic examination showed acute and chronic inflammation of the urachal cyst. The post-operative course was non specific and there was no evidence of wound infection.