A case of a young man with fever of unknown origin is presented. This diagnosis can be frustrating for both patients and physicians because the diagnostic workup often involves numerous noninvasive and invasive procedures that sometimes fail to explain the fever. In the presented case some of the imaging diagnostic findings suggested malignant hematological disorder. However, histopathological and microbiological investigation proved vertebral osteomyelitis caused by Staphylococcus haemolyticus. Diagnosis was established by positron emission tomography, magnetic resonance imaging, and culture and histopathological analysis of a spinal biopsy. 3 months of antibiotic therapy was curative. Biopsy and microbiological investigation may be necessary in patients with fever, back pain and evidence of a spinal lesion on imaging, even if neoplastic disease is suspected.