Pseudohypoaldosteronism was first described in 1958 by Cheek and Perry, who reported an infant with severe salt wasting in the absence of any renal or adrenal defect. Since then several reports have described patients affected by symptoms consistent with resistance to mineralocorticoid action. The clinical picture is characterized by salt wasting and failure to thrive and is resistant to the administration of exogenous mineralocorticoids. Biological features are invariably high plasma and urinary aldosterone levels and elevated plasma renin activity associated with hyponatremia, hyperkalemia, and metabolic acidosis. The discovery of abnormal binding of aldosterone to the mineralocorticoid receptor (MR) in lymphocytes from affected patients, by analogy to findings in other syndromes of steroid hormone resistance, led to the hypothesis that the disease reflected a molecular defect in MR, which has prompted a series of molecular studies to characterize the defect. In this paper we review mechanisms of mineralocorticoid action, discuss the clinical features of mineralocorticoid resistance, overview the molecular characterization of the MR, and close with some pathophysiological hypotheses and questions.