purpose: to report a case of erdheim-chester disease with bilateral orbital involvement and to inform ophthalmologists about this uncommon condition. methods: case report. a 41-year-old man presented with proptosis, lid xanthelasmas, disc edema and extraocular muscle restrictions. he was suspected of having a systemic lymphoma and had already been submitted to a retroperitoneal biopsy, however, the diagnosis was still uncertain. results: the patient was evaluated by computed tomography and magnetic resonance imaging of the orbit. orbital pseudotumor was suspected and a biopsy of the orbital lesion initially failed to provide the correct diagnosis which was only made after detailed analysis of the clinical and imaging findings, and review of the histopathologic studies. the systemic diagnosis was made after the orbital diagnosis although the patient had been extensively investigated for more than one year. conclusions: erdheim-chester disease is a rare idiopathic systemic condition characterized by a xanthogranulomatous process involving retroperitoneum, heart, lungs, bone and other tissues. the condition is often fatal due to renal or cardiovascular complications. ocular findings are rare but may be very helpful for the diagnosis. therefore, ophthalmologists should be aware of the clinical manifestations and imaging findings of this rare disease in order to establish an early diagnosis.