We report one case of adult-onset Still's disease. The diagnosis of this disease currently requires application of Yamaguchi's criteria and then exclusion of infectious, haematological, autoimmune and neoplasic disorders. The place of biology is enhanced with the use of new markers like ferritin and glycosylated ferritin. Low percentage of glycosylated ferritin (<20%) in presence of very high level of ferritin, unexplained prolonged fever with leukocytosis can help to diagnosis. However, glycosylated ferritin is not yet of in routine use.