There are three types of histiocytosis: eosinophilic granulomatosis, Hand-Schuller-Christian disease, and Letterer-Siwe disease. Among them, eosinophilic granuloma accounts for 60-80%. The diagnosis is as follows: (1) It occurs in children and adolescents, and the common sites are the skull, spine, ribs and femur. Those occurring in long bones are found in the diaphysis and epiphysis. (2) Clinical symptoms are highly variable and can be asymptomatic or painful, swollen and dysfunctional, and pathological fractures can occur. (3) Hematologic examination shows increased white blood cell and eosinophil counts. (4) X-rays show well-defined but irregular round or oval areas of hypodensity. The bone cortex may be invaded, thinned and slightly swollen if it occurs in the backbone, and reactive periosteal new bone formation may occur. If it occurs in the vertebral body, the vertebral body may be compressed into a flat vertebra, and sometimes it may protrude backward into the spinal canal to produce spinal cord or nerve compression. (5) Pathological examination: The main lesions are proliferating histiocytes, which are mixed with eosinophils, lymphocytes, foam cells, plasma cells, neutrophils and fibroblasts. It is often accompanied by secondary hemorrhage, necrosis, cystic degeneration and pathological fracture.