Apparent mineralocorticoid excess is a syndrome reflecting the absent or impaired activity of the enzyme 11β-hydroxysteroid dehydrogenase Type 2. It may be mild when the mutant enzyme retains some activity, or severe when activity is absolutely or essentially absent. Diagnosis relies on a triad of hypertension, hypokalemia and suppressed plasma aldosterone levels, plus an abnormal urinary cortisol to cortisone ratio, either free steroid or metabolites. Treatment is symptomatic in the mild form - correction of hypertension and hypokalemia - but needs to be prompt, vigorous and sustained in the severe form, which usually presents in neonates/infancy. Elucidation of the pathogenesis of apparent mineralocorticoid excess is an example of 'reverse translation', in that it proved prismatic for the demonstration of the physiologic mechanisms underlying the selective activation of epithelial mineralocorticoid receptors by aldosterone.