This is a case report involving diagnostic errors that resulted in the death of a 15-year-old girl, and commentaries on the case from her parents and involved providers. Julia Berg presented with fatigue, fevers, sore throat and right sided flank pain. Based on a computed tomography (CT) scan that identified an abnormal-appearing gall bladder, and markedly elevated bilirubin and "liver function tests", she was hospitalized and ultimately underwent surgery for suspected cholecystitis and/or cholangitis. Julia died of unexplained post-operative complications. Her autopsy, and additional testing, suggested that the correct diagnosis was Epstein-Barr virus infection with acalculous cholecystitis. The correct diagnosis might have been considered had more attention been paid to her presenting symptoms, and a striking degree of lymphocytosis that was repeatedly demonstrated. The case illustrates how cognitive "biases" can contribute to harm from diagnostic error. The case has profoundly impacted the involved healthcare organization, and Julia's parents have become leaders in helping advance awareness and education about diagnostic error and its prevention.