Background: Hydrometrocolpos due to vaginal atresia is a rare congenital anomaly characterized by an abdominal mass; girls with this anomaly are prone to develop obstructive uropathy due to compression of bladder and/or urethra.

Case: We report the case of a two-month-old girl who presented with an abdominal mass and dysuria. She was found to have a lower vaginal atresia and hydrometrocolpos by MRI. She was successfully treated surgically by reconstruction of vagina and drainage of 100 ml serosanguinous fluid. Summary and Conclusion: Early diagnosis and surgery reduces the incidence of complications such as infection, rupture and renal failure. Diagnosis may be suspected prenatally by ultrasonography and confirmed postnatally by magnetic resonance imaging.