Adrenocortical carcinoma is an extremely rare cause of hyperal-dosteronism and accounts for fewer than 2% of aldosterone-producing tumors.52,52a Although aldosterone may be the only adrenal steroid overproduced early in the course of the disease, hypersecretion of cortisol usually occurs at some point. Occasionally, overproduction of adrenal androgens may occur. The circadian rhythm of plasma aldosterone levels, commonly seen in patients with an adenoma, is absent in patients with adrenal carcinoma, presumably because ACTH has little effect on aldosterone secretion by malignant tumor cells.