Intraperitoneal free air in a child with acute lymphoblastic leukemia (ALL) treated with induction chemotherapy is an ominous sign suspective of gastrointestinal perforation. We report a case of pneumatosis cystoides intestinalis (PCI) with free intraperitoneal air without bowel perforation in a child with Down syndrome during ALL induction treatment. PCI is a physical sign characterized by gas-filled cysts of the submucosa or subserosa of the bowel that can lead to pneumoperitoneum. Clinical management of this case in respect to reported literature on PCI and specific characteristics of patients treated with ALL induction chemotherapy are discussed.