Fever of unknown origin (FUO) is categorized into four etiological groups: infections, neoplasms, non-infectious inflammatory diseases, and miscellaneous conditions. We often have difficulties in diagnosing prolonged fever in our daily medical practice. Prolonged fever involving the neck also consists of these etiological categories, and the diagnosis is confirmed with a detailed clinical history, physical examination and some appropriate tests including imaging studies. This paper focuses on diagnostic imaging of the neck associated with prolonged fever, and shows typical images of representative diseases, such as various types of abscess, malignant lymphoma and Kawasaki disease. Diagnostic imaging may lead to the accurate diagnosis, and provide essential information for proper treatment.