SummaryThe clinical interest of this case resides in the fact that the surrenal insufficiency was preceded by symptoms of myxœdema whereas habitually, in the Schmidt syndrome, the thyroïd lesions are only found at necropsy. Moreover, this observation shows the noxious role of thyroxine in diseases where there is a latent state of surrenal insufficiency.The pathological study shows that between cases of death from Addison disease and cases of Schmidt syndrome there are only degrees in the thyroïd alterations. These alterations picture at the same time the influence exerted by destruction of surrenal cortex, on the parenchyme of the thyroïd and on the lymphoïd tissue. We believe we have shown that the massive lymphocytic infiltration of the thyroïd is only a particular instance of the lymphoïd hyperplasia due to the lack of cortical hormones.