Langerhans cell histiocytosis (LCH) is a rare group of diseases of unknown etiology and pathogenesis, characterized by proliferation of Langerhans cells in the monocyte-macrophage system, with a highly heterogeneous clinical presentation. The 2008 WHO classification of hematopoietic and lymphoid tumors classifies it as a subtype of histiocytic and dendritic cell tumors. Based on the common presence of pathological LC cells, the previous names “histiocytic proliferative disease X”, eosinophilic granuloma of bone, Han-She-Co disease, and LCH have been replaced by LCH. The disease can occur at any age, but the peak age is 1-3 years old. Clinical manifestations vary depending on the number and location of organs involved, and commonly include rash, bone pain, proptosis, hepatosplenomegaly, etc. Systemic symptoms include fever, emaciation, diarrhea, edema, dyspnea, irritable thirst and polyuria. Patients may present with single site or organ lesions, or with multi-site or multi-organ multisystem lesions. The diagnosis of LCH is based on the presence of LC cells confirmed by tissue biopsy of the involved organs, especially positive staining for CD1a, CD207 and S-100 has diagnostic value.In 1987, the International Society of Histiocytes classified the diagnosis of LCH into three levels of confidence: preliminary diagnosis, diagnosis and confirmation. A preliminary diagnosis can be made based on clinical manifestations, laboratory and X-ray examinations, and general pathology findings. Confirmation requires light microscopic visualization of the lesioned cells plus positive intracellular Birbeck particles and/or immunohistochemical CD1a monoclonal staining on electron microscopy. Because of the heterogeneous clinical presentation of LCH, it should be differentiated from other types of histiocytic diseases such as histiocytic sarcoma (i.e., malignant histiocytosis) and disseminated juvenile yellow granuloma, and especially from related diseases with bone disease, skin lesions, and organ enlargement, such as myeloma, lymphoma, metastatic carcinoma, neuroblastoma, tuberculosis, psoriasis, and pituitary inflammation. The prognosis regarding LCH is mostly based on the Lavin-Osband grading method: 1 point for age ≤2 years, 1 point for ≥4 organs involved, and 1 point for impaired organ function. Grade I is 0, grade II is 1, grade III is 2, and grade IV is 3. The higher the score, the worse the prognosis, indicating that the age of onset, the number of involved organs and impaired function are closely related to the prognosis. In general, bone involvement has a better prognosis than extraosseous tissue involvement, isolated bone involvement has a better prognosis than multiple bone involvement, and multi-system multi-organ involvement has the worst prognosis. In the diagnosis of LCH, the involved organs can be classified as high-risk and low-risk: high-risk organs include liver, spleen, lung, and bone marrow, and low-risk organs include skin, bone, lymph nodes, and pituitary gland. The above grading and stratification is a guide for prognosis determination and treatment plan selection. Treatment options for LCH are based on disease stratification, with prednisone combined with vincristine or lesion scraping for low-risk patients, systemic chemotherapy (CEOP or FMD regimens, etc.) for high-risk patients, salvage therapy including cytarabine and cladribine, and hematopoietic stem cell transplantation if available. Other drugs such as pamidophosphate, cyclosporine, interferon, and thalidomide may be tried, but their efficacy is uncertain. It is recommended to refer to the relevant treatment protocols provided by the International Society of Tissue Cells. The eradication rate of treated low-risk children can reach 99%, but the long-term survival rate of high-risk patients is only about 35%. The difficult case selected for this issue is an adult patient with LCH, which is highly susceptible to underdiagnosis and misdiagnosis due to its low adult prevalence (approximately 1-2 per million) and lack of specificity in clinical presentation. In this case, the patient had been treated for 13 years for simple central uremia, and a definitive diagnosis was obtained only after the discovery of an occupying thyroid lesion and multiple bone destruction and a pathological tissue biopsy. This case suggests that when we encounter clinical symptoms such as dyspnea, thirst, polyuria, bone pain, emaciation, fever, loosening or loss of teeth, ataxia, and poor memory, as well as signs such as rash, scalp nodules, local soft tissue edema due to bone destruction, lymph node enlargement, gingival hyperplasia, or hepatosplenomegaly, we should be aware of the possibility of LCH. Patients who develop uremia alone should be followed up closely to observe the presence of characteristic manifestations of LCH to make early diagnosis.