A 9-year-old girl presented with systemic-onset juvenile idiopathic arthritis, diagnosed at 3.5 of age and which was difficult to control despite several therapeutic trials. Five years after diagnosis of juvenile idiopathic arthritis, nephrotic proteinuria was noticed. Renal biopsy confirmed the diagnosis of amyloidosis, and chlorambucil was initiated, with general improvement of the disease and reduction of proteinuria.