SummaryA case of plasma-cells thyroiditis is described. The plasma-cells infitration precludes its classification among the usual chronic thyroiditides.According to the work of Doniach and Witebsky the pathogenic basis of this thyroiditis could be an auto-immunological process. Serologic tests performed in this case have proved this assumption.The necessity of early therapy with corticoids is stressed with the hope of inhibiting the«chain reaction»leading to the destruction of the gland.