Defects of the urachus obliteration may lead to urachal abnormalities such an urachal cyst, which tend to rest asymptomatic. We report a case of a four-old-year boy who referred a three-week history of abdominal pain, dysuria and fever. A hypogastric mass was observed at the exploration. The ultrasonography and the computed tomography were compatible with an infected urachal cyst. Intravenous antibiotic therapy was started, with an optimal response. Four months later, a chirurgical complete excision of the urachal cyst was performed. Among different congenital disorders of the urachus, urachal cysts and patent urachi are the most frequent. Urachal cysts may become infected, causing suprapubic pain, dysuria, fever and abdominal mass, as well as signs of peritonism. The main tool for diagnose these lesions is ultrasonography. They could potentially degenerate into adenocarcinoma in adults, which is rare but associated to bad prognosis. Urachal remnants have been classically managed surgically. However, an active surveillance of these lesions with a conservative treatment could be an alternative, since spontaneous resolution is more common than previously thought.