A 36-year-old woman with Cushing syndrome was evaluated for coexisting hyperaldosteronism, which was suggested by an abnormal response of the aldosterone-to-cortisol ratio in peripheral blood to the ACTH-administration despite a low basal aldosterone-to-renin ratio. Computed tomography revealed two independent tumors in the left adrenal gland, and adrenal venous sampling indicated hyperaldosteronism in addition to hypercortisolism in the same side. Postsurgical study including immunohistochemical analysis of steroidogenic enzymes suggested one adenoma to be cortisol-producing and the other, aldosterone-producing. The comorbidity of these different hormone-producing adenomas is not rare and careful pre-surgical evaluation is necessary to avoid post-surgical exacerbation of latent hyperaldosteronism.