A 25-year-old patient presented with fever over a period of more than three months, night sweats, fatigue and a weight loss of more than 10 kg. A splenomegaly and an enlargement of cervical, thoracic and abdominal lymph nodes were found. The suspected malignant hematologic disorder could not be confirmed. Instead, epithelioid noncaseating granulomas in the bone marrow and a cervical lymph node as well as an elevated serum ACE and a lymphocytic alveolitis were found. These findings led us to the conclusion that the patient was suffering from sarcoidosis. Treatment with corticosteroids resulted in complete regression of all symptoms, including the splenomegaly and the enlargement of the lymph nodes. Sarcoidosis is an important consideration in differential diagnosis of fever of unknown origin, even in the absence of pathological changes on X-ray films of the chest.