Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 8 6 2024 09 29 247 251 Mohsen Jafari Department of Pediatric Infectious Diseases, Bahrami Children Hospital, Tehran University of Medical Sciences, Tehran, Iran Maryam Ghodsi Department of Pediatric, Bahrami Hospital, Tehran University of Medical Sciences, Tehran, Iran Maryam Noory School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Mahdieh Mousavi Torshizi Bahrami Children’s Hospital, Tehran University of Medical Sciences, Tehran, Iran Mohammad Kaji Yazdi Pediatric Hematology and Oncology Department, Bahrami Children’s Hospital, Tehran University of Medical Sciences, Tehran, Iran 2023 08 06 2024 02 21 Hemophagocytic lymphohistiocytic syndrome is a rare, significant, and life-threatening disease. We are reporting this case with the hope that it may contribute to saving some patients if treated appropriately. A 4-year-old boy presented with fever and pancytopenia. He was treated based on the symptoms that matched the criteria of (HLH). Furthermore, the bone marrow biopsy report revealed the presence of Leishman’s bodies.Hemophagocytic lymphohistiocytic syndrome is a rare, important and life-threatening disease that we are reporting this case due to the hope of saving some patients if treated. A 4-year-old boy with fever and pancytopenia, who was treated according to the symptoms matching the criteria of HLH, as well as the bone marrow biopsy report showing Leishman’s bodies.HLH is a life-threatening disease based on cumulative increase and unrestricted excessive activity of T lymphocytes, cytokines and macrophages, which occurs in two primary and secondary forms, which requires the rejection of all risk factors, symptoms similar to the disease, including infections, lymphoproliferative and autoimmune diseases and other causes, and after ruling out other causes, the patient should be treated quickly with the treatment protocol of this disease, which is reported.due to the rarity of this disease and the urgent need for timely diagnosis and treatment; we are trying to report this patient. https://crcp.tums.ac.ir/index.php/crcp/article/view/856 https://crcp.tums.ac.ir/index.php/crcp/article/download/856/590