A growing body of evidence suggests that hyperaldosteronism contributes significantly to the development and the severity of hypertension as well as to resistance to antihypertensive treatment. In cross-sectional analyses, plasma aldosterone levels have been shown to relate to BP levels, particularly in obese individuals. In these same individuals, BP was not related to plasma renin activity, suggesting an effect of aldosterone on BP independent of renin–angiotensin II. In a recent prospective analysis from the Framingham investigators, baseline serum aldosterone was strongly associated with development of hypertension during a 4-yr follow-up. Historically, primary aldosteronism has been thought to be an uncommon cause of hypertension. Recent studies, however, suggest that 10 to 15% of individuals with hypertension fulfill the biochemical criteria for primary aldosteronism. Demonstration of such a high prevalence of primary aldosteronism in patients with presumed primary hypertension suggests that aldosterone excess is a common contributing cause to the development of hypertension.