We describe the clinical course of a 24-year old male with Crohn’s disease in immunosuppressive therapy admitted with a 6-week history of fever, weight loss, night sweat, and general malaise. The patient received extensive workup for a fever of unknown origin and received empiric antibiotics. Workup with Fluorine-18 fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) positron-emission tomography (PET/CT), and magnetic resonance imaging (MRI) with intravenous contrast showed multifocal ostitis of the columna and os sacrum, as well as abscesses in m. iliopsoas and m. iliacus and affection of the retroperitoneum, liver, and spleen. Initially, malignancy was suspected, but a subsequent liver biopsy showed necrotizing granulomatous inflammation and a later polymerase chain reaction (PCR) showed Bartonella henselae. The patient had relevant exposure from housecats. He was treated with Doxycycline and Rifampicin for 12 weeks resulting in complete recovery. This case is, to our knowledge, a rare example of disseminated infection with Bartonella henselae visualized on both [¹⁸F]FDG-PET/CT and MRI.