Fever of unknown origin (FUO) is both a clinical and a diagnostic challenge. Furthermore, an FUO case with isolated marrow noncaseating granuloma can further confound diagnosis. However, these two findings together may help narrow down the pathological possibilities. This article presents a case report of FUO and lymphopenia for 2 months. Multiple studies to evaluate infectious etiology were unremarkable. Bone marrow biopsy revealed isolated bone marrow granuloma, suggestive of sarcoid. The patient responded well to glucocorticosteroids with resolution of lymphopenia. Sarcoid should enter the differential of lymphopenia and FUO even without lymphadenopathy or abnormal chest radiography. This article provides a of review of CD4 lymphopenia, noncaseating granuloma of the marrow, and sarcoidosis.