A 61-year-old male patient with a 15-day history of dull pain in the left chest was admitted to our hospital. He had a 6-year history of hypertension and was treated with valsartan and amlodipine tablets every day. Upon laboratory examination, the T-cell spot of tuberculosis assay (T-SPOT.TB) was positive and other laboratory indicators were normal. No obvious abnormalities were found in physical examination. Plain chest CT showed an osteolytic lesion in the left fifth rib. To evaluate the extent of skeletal lesions, 99mTc-MDP SPECT was performed. A lesion with high uptake of 99mTc-MDP in the left fifth rib was revealed and no other lesions were found in the image (Figure 1). These two imaging examinations suggested that the lesion might be malignant process. Therefore,18 F-FDG PET/CT was performed for staging. PET/CT image showed obvious osteolytic bone destruction and abnormal FDG uptake (SUVmax 14.5) in the left fifth rib with local soft tissue mass formation (Figure 2). With no other malignant signs found on PET/CT, the patient underwent a rib biopsy to confirm the diagnosis. Unexpectedly, histopathological examination suggested that the lesion was an eosinophilic granuloma. LCH was considered. Subsequently, the lesion was approached through a left posterolateral thoracotomy, and part of the fifth rib was excised with the lesion. By immunohistochemistry stain, the cells of surgical specimens were positive for CD1a, S-100, and Langerin, which confirmed the diagnosis of LCH (Figure 3). The patient is currently in good health condition without chest pain after the operation and does not present any complications during follow-up. The relevant images are shown in Figure 4.