Abstract
Still's disease, also known as systemic juvenile idiopathic arthritis (SJIA), and acute lymphoblastic leukemia have similar clinical and biological features posing diagnostic and treatment challenges. Indeed, while Still's disease is a diagnosis of exclusion in rheumatology, polyarthritis associated with hyperleukocytosis and fever, which is characteristic of this disease, are often detected in early stages of acute lymphocytic leukaemias. We here report the case of a 4-year-old girl, treated for Still's disease, in whom the diagnosis of acute lymphoblastic leukemia was made after 2 months, based on bone marrow biopsy.