A 50 year old man is described in whom primary hypothyroidism and isolated ACTH deficiency leading to adrenocortical insufficiency occurred simultaneously. Low thyroid hormone levels, elevated serum TSH values and high titers of antithyroid antibodies (ATA) were consistent with primary hypothyroidism. The diagnosis of secondary adrenocortical insufficiency was based on low cortisol and ACTH morning levels, low urinary steroids, a significant increase of cortisol levels after 0.25 mg tetracosactide iv, an absence of ACTH and cortisol release after insulin-induced hypoglycemia and a similar absence of ACTH and 11-deoxycortisol increase after metyrapone administration. After one year treatment and five days withdrawal of cortisol administration, the insulin-induced hypoglycemia still failed to elicit secretory responses of ACTH and cortisol, despite the normalization of thyroid hormone levels. The etiopathogenesis of these two coexisting endocrine deficiencies is discussed.