Results Among 960 cases fulfilled the definition. 828 (86%) were diagnosed as having diseases of known causes. 190 (23%) were infectious diseases (acute focal bacterial nephritis 31, cat-scratch disease 23, urinary tract infection 20, osteomyelitis 9 and tuberculosis 8), 447 (54%) were rheumatic diseases (JIA 221, vasculitis syndrome 39, inflammatory bowel diseases 34, SLE 25, and MCTD 12), 67 (8%) were leukemia/malignancy (acute lymphatic leukemia 38, malignant lymphoma 9, neuroblastoma 4, Castleman disease 3). Autoinflammatory syndrome was diagnosed in 89 cases (PFAPA 45. FMF 17, CINCA 9, HIDS 9, and others). Other diseases included subacute necrotizing lymphadenitis, hemophagocytic syndrome, drug-induced fever, and ADEM. Conclusion Rare infectious diseases such as cat-scratch disease and tuberculosis were reminded in addition to routine investigation of infection. Along with these work-ups, malignancies and rheumatic diseases should be investigated. To have final diagnosis of auto-inflammatory syndrome, clinical characteristics such as fever pattern, skin rash, arthritis, and genetic analysis are needed. We established an algorism as a clinical decision support system for diagnosis. from 15th Paediatric Rheumatology European Society (PreS) Congress London, UK. 14–17 September 2008