Lung cavitary lesions are a rare finding in the nontransplant setting of a patient with acute leukemia. Among viral agents, cytomegalovirus (CMV) may cause pulmonary nodules and cavities in patients undergoing hematopoietic stem cell transplantation, but during pediatric acute lymphoblastic leukemia treatment, CMV disease is less common. Here we report the case of a boy affected by acute lymphoblastic leukemia who suffered severe cavitary CMV pneumonia during chemotherapy, and we review the current literature.