Background: Osteonecrosis is a problem that can happen when children with acute lymphoblastic leukemia (ALL) are being treated. The aftereffects of osteonecrosis are one of the most serious long-term complications for children being treated for acute lymphoblastic leukemia. The goal of this study is to examine how often and why osteonecrosis worsens in young patients with leukemia. Specifically, the study will focus on the hip bone.Patients and Methods: This study looked at patients who had a bone condition called osteonecrosis of the femoral head. They were identified using MRI scans and their images were checked using an electronic system called PACS. We did not include patients who were lost to follow-up or who did not have regular MRI screenings. We also did not include patients who had ON but it was not caused by childhood acute lymphoblastic leukemia. Examples of other causes include lymphoma, trauma, infection, slipped capital femoral epiphysis, or Legg– Calve´–Perthes disease. We also excluded patients who had less than one year of follow-up after their treatment ended.