Clinical, biochemical and molecular data on five kindreds with dexamethasone-suppressible hyperaldosteronism are reviewed. The clinical phenotype varies from severe, early onset hypertension to much milder blood pressure elevation; hypokalaemia is usually mild. The genetic basis of the syndrome reflects the presence of a chimaeric gene derived from an unequal crossover between CYP11B1 and CYP11B2, resulting in ACTH-sensitive aldosterone synthase activity. In five kindreds, at least three different mutations have been identified, suggesting that allelic predisposition might lead to increased geographical prevalence of the condition in Celtic populations.