Evaluation of abdominal pain in children can be often difficult. Acute appendicitis is the most frequent disease in children population that often requires a surgical intervention. Only 2% of operated children belong to the group younger than 3 years. Appendicitis in young children can be considered as a diagnostic challenge and it is characterized by: atypical clinical course, late diagnosis, high percentage of perforations or other complications (e. g. abscess formation and peritonitis), as well as high level of mortality and morbidity rates. Fever is often an associated symptom: particularly children between 6 months - 36 months of age with persistent fever and laboratory tests compatible with not localized bacterial infection can be carefully evaluated both with clinical examination and radiological imaging. Ultrasonography is simple, non invasive, easy to use, and applicable in a wide variety of clinical situations such as for the differential diagnosis of fever of unknown origin (e.g. local nephritis, hepatic or splenic abscess). The article reports the case of a 14-month-old child with persistent and unknown fever caused by an appendicular abscess treated successfully with percutaneous drainage. The rarity of the case with its unusual presentation, including unexplained prolonged fever and absence of chronic abdominal pain, confirms that discerning the correct diagnosis can be very challenging and therefore clinicians should always be careful. The recommendation is “to admit, observe and think broadly” in all suspected cases.