We report two cases of severe hypertension and unilateral renal dysplasia. No renal artery stenosis and no other urogenital malformations were found. In both cases we found substantially enhanced secretion of renin from the dysplastic kidney. After nephrectomy both patients obtained a distinctive and permanent reduction or normalization of blood pressure. In the two cases reported, regional renin release induced by ischemia is a very likely etiological factor.