Abstract: The present invention relates to an in vitro method for evaluating the prognosis of an autoimmune or chronic inflammatory disease in an individual, comprising the following steps: a) determining (i) the level of an anti-IL-17 autoantibody and/or (ii) the level of an [IL-17/anti-IL-17 autoantibody] complex in a biological sample of the individual, and b) comparing the level of autoantibody and/or of complex determined in step a) with a reference value, the comparison being indicative of the prognosis of an autoimmune or chronic inflammatory disease in said individual.