Systemic juvenile idiopathic arthritis (sJIA, also known as Still's disease) is a rare auto-inflammatory disease presenting in children under 16 years of age and accounts for 10% of all types of juvenile idiopathic arthritis. It is the most severe subtype with significant morbidity and even mortality. 1 The reported prevalence of sJIA varies between 7-150 per 100.000, and incidence numbers vary between 1 and 22 per 100.000 per year. 2 This case report illustrates diagnostic challenges in young children, discusses considerations with respect to laboratory testing and physical examination of joints, and highlights a possible role of FDG-PET/CT in diagnosing cases where classical features are not (yet) present. | CASE PRESENTATION | Case 1-History and examinationA 5-year-old girl was referred to our clinic with fever for six days, non-productive cough and general malaise despite amoxicillin treatment for two days. Past medical history was uneventful. She complained of diffuse pain in the lower extremities. Physical examination showed slight wheezing at auscultation and no other abnormalities. Laboratory blood tests and a lung X-ray revealed elevated infectious parameters and a possible consolidation (Table 1). The most probable diagnosis was thought to be a bacterial pneumonia or viral infection. Serological