A 67-year-old male with no significant medical history visited a nearby hospital after 10 days of fatigue and fever. Blood test results indicated an acute inflammatory response, including elevated C-reactive protein (CRP) levels and neutrophilia, while contrast-enhanced computed tomography (CT) scan findings showed swelling of the bilateral mediastinal and hilar lymph nodes. The patient was referred to our hospital for further examination and treatment. Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) of the left hilar lymph node showed only histiocytic infiltration, whereas surgical biopsy results revealed multinucleated giant cells and early phase granuloma. A surgical biopsy of the left-sided lung (S⁵), which had mild gallium accumulation, also showed multinucleated giant cells and granuloma. Based on the pathological results, we diagnosed acute sarcoidosis and performed corticosteroid administration. Following treatment, both symptoms and examination findings, such as chest CT scan, spirometry and blood test results, dramatically improved.