Fever of unknown origin (FUO) presents a major diagnostic challenge as it is a consequence of many infectious as well as malignant, rheumatologic and other diseases. Here we present the case of a woman with mediastinal and abdominal lymphadenopathy who was initially suspected to have lymphoproliferative disease, but our histopathologic examination revealed sarcoidosis. Sarcoidosis, especially chronic, is a rare cause of FUO, because it usually manifests as a febrile condition. A woman presented with shoulder and ankle joint pain, mediastinal and abdominal lymphadenopathy and fever at the Infectious Diseases Clinic. Physical examination identified the presence of lupus pernio and normal respiratory noise in the lungs, and later peripheral lymphadenopathy. Peripheral blood smear indicated conspicuous eosinophilia. Biopsy examination obtained by rigid bronchoscopy suggested pulmonary sarcoidosis. Sarcoidosis and lymphoma may have similar clinical manifestations; both present as mediastinal and abdominal lymphadenopathy with constitutional symptoms. Therefore, in the diagnosis of sarcoidosis, it is important to exclude lymphoproliferative diseases and other granulomatous diseases.