Establishing a diagnosis in cases of fever of unknown origin (FUO) in immunocompromised patients can be difficult. In 25-35% infectious diseases are the underlying cause. This article reports the case of a 74-year-old woman with a 5-month history of fever. Through open biopsy of the femoral shaft and microbiological analysis, a diagnosis of neoehrlichiosis could be established. After initiation of treatment with doxycycline, the symptoms quickly resolved resulting in a complete recovery.