Fulminant hepatitis is a rare complication of adenoviral infection that has not previously been reported in children receiving standard chemotherapy for acute leukemia. The authors have observed fatal adenovirus hepatitis in three children receiving first-line chemotherapy for acute lymphoblastic leukemia (ALL). The patients presented 10, 17, and 8 months into therapy according to the UKALL XI (third intensification), UKALL 97/99 (maintenance), and pilot UKALL 2003 (delayed intensification II) protocols, respectively. All patients received aggressive supportive care and intravenous immunoglobulins. The second and third patients were also treated with intravenous cidofovir. Despite these measures, all three children deteriorated rapidly and died of fulminant liver failure. Although rare, adenovirus infection should be considered in the differential diagnosis of acute hepatitis in children receiving standard chemotherapy for ALL.