The fever of unknown origin from time to time constitutes a serious clinical problem and nearly all diagnostic methods are involved to discover urgently its cause. According to literature data (18)F-fluoro-deoxyglucose PET/CT was successful in 25-70% of cases even in patients without any positive findings with conventional diagnostic techniques. The Hungarian National Health Fund does not include fever of unknown origin in the list of reimbursed (18)F-fluoro-deoxyglucose PET/CT indications. The authors try to illustrate the clinical problem with this case report. Fever of unknown origin persisted in a patient for a year, but conventional diagnostic procedures were unsuccessful to find the cause of the fever. Finally, (18)F-fluoro-deoxyglucose PET/CT indicated a metabolically active focus between the pancreas tail and the spleen. After a long-lasting antibiotic therapy the patient became symptomfree.