We report the case of a 42-year-old woman who was admitted in 2002 for exploration of diffuse bone pain. She had medical history of pulmonary tuberculosis. Her current symptoms had started 9 months earlier and consisted of bone pain, affecting the legs. She had asthenia and weight loss. At admission, physical examination showed bilateral and symmetrical long bone pain, especially the knees and the ankles. Physical exam was normal elsewhere. Laboratory tests showed inflammation, with an erythrocyte sedimentation rate of 90 mm/h and C-reactive protein 8 mg/l. Protein electrophoresis, red and white blood cell count, renal, and liver function tests were normal. Serum calcium, phosphorus, and urinary calcium were normal. Radiographs showed multiple mixed bone lesions with sclerotic and lytic areas of the femora, tibiae, humerus. Chest radiographs and thoracic computed tomography (CT) scan showed pulmonary fibrosis. Biopsy of the tibial area displayed foamy lipid-laden histiocytes, confirming the diagnosis of Erdheim-Chester disease. Patient was treated with prednisolone plus cyclophosphamide. Her clinical condition improved remarkably during 4 years, but she developed acute renal failure leading to death.