One percent of all pregnancies are found to have an antenatal abnormality; of these, 20% involve the genitourinary system. Today, controversy still exists regarding the postnatal management of some antenatal abnormalities detected by ultrasound. We present a case in which antenatal hydronephrosis initially detected by ultrasound appeared to resolve in utero. Postnatally, the child developed Citrobacter diversus urosepsis, meningitis, and cerebral abscess. Voiding cystourethrogram obtained after resolution of sepsis revealed grade IV reflux. This case underscores the importance of a full postnatal evaluation for all children with antenatal hydronephrosis and alerts clinicians to a virulent pathogen not commonly associated with urinary tract infection.