A case of a young woman with the syndrome of primary aldosteronism and malignant ovarian tumor is reported. Hormone studies revealed extremely high urinary aldosterone, undetectable plasma renin activity, elevated plasma 17beta estradiol and testosterone, and low plasma FSH and LH. Plasma cortisol and urinary 17-hydroxycorticoids were at the upper normal limits. Autopsy disclosed an ovarian tumor, histologically an arrhenoblastoma, with polymorphic aspects. The adrenal glands grossly were normal. Aldosterone was found by the double radioisotopic technique in the neoplastic tissue.