A 5(3/12)-year-old boy with Philadelphia chromosome (+) pre-B acute lymphoblastic leukemia (ALL) without extramedullary involvement did not achieve remission after induction therapy. His family stopped therapy, but he was readmitted eight months later due to pyoderma, pneumonia and active leukemia with leukocytosis. During cytoreductive and antibiotic therapy, he developed progressive abdominal distension, pain, globe vesicale, tachypnea, and respiratory alkalosis. Bowel sounds could not be auscultated. Dilation, mainly in the large intestine, was detected radiologically. His neurological examination revealed absence of superficial reflexes and hypoesthesia along with normal motor strength and deep tendon reflexes in the lower extremities, consistent with conus medullaris syndrome, which was thought to give rise to acute colonic pseudo-obstruction.