Rationale:Eosinophilic granuloma (EG) – the most common form of Langerhans cell histiocytosis – occurs rarely, and manifestations with only rib and clavicle involvement are extremely rare. EG symptoms often include pain, swelling, and soft tissue mass. The clinical diagnosis of bone EG is complex, and the differential diagnosis includes Ewing sarcoma, tuberculosis, multiple myeloma, lymphoma, primary bone malignancy, and other osteolytic lesions.Patient’s concern:The patient was an 11-year-old female who found a subcutaneous mass at the junction of the right clavicle and sternum 2 days before presenting at the clinic without apparent triggers. Initially, we considered a subcutaneous cyst or inflammatory mass. Color ultrasound and computed tomography examination revealed osteomyelitis. Finally, the patient was diagnosed with EG after a pathological tissue biopsy, and the child recovered after surgery and anti-infective treatment.Diagnosis:The patient underwent surgery to remove the tumor at a specialist hospital and was diagnosed with EG by pathological examination.Intervention:The patient went to a specialist hospital for surgery to remove the mass and underwent anti-infective treatment.Outcomes:The patient recovered after surgical resection and antibiotic treatment.Lessons:In this report, we emphasize that the clinical presentation of EG in children is not specific. Furthermore, examining age, history, presence of symptoms, and the number of sites is essential to make a correct diagnosis, and a histological examination is necessary to confirm the diagnosis.