Familial hyperaldosteronism (FH) encompasses 3 types of autosomal dominant hyperaldosteronisms leading to inheritable hypertension. FH type II (FH-II), undistinguishable from sporadic hyperaldosteronism, represents the most frequent cause of inheritable hypertension and is believed to only manifest in adults. FH-III is a severe variety of PA resistant to pharmacotherapy and recently demonstrated to be caused by mutations in the gene encoding the potassium channel KCNJ5. In this report, we describe a FH pediatric patient, remarkable both for age at onset and unusual presentation: a two-years old girl with polyuric-polydipsic syndrome and severe hypertension, successfully treated with canrenone and amiloride. The girl had severe hypertension, hypokalemia, hypercalciuria, suppressed renin activity, high aldosterone, and unremarkable adrenal imaging. FH type I was ruled out by glucocorticoid suppression test, PCR test for CYP11B1/CYP11B2 gene, and urinary 18-oxo-cortisol and 18-hydroxy-cortisol excretion, which was in FH-II range. In spite of a clear-cut FH-II phenotype, the girl and her mother were found to harbor a FH-III genotype with KCNJ5 mutation (c.452G>A). Treatment with canrenone was started, resulting in prompt normalization of electrolytes and remission of polyuric-polydypsic syndrome. The addition of amiloride led to a complete normalization of blood pressure. This report expands the phenotypic spectrum of FH-III to a milder end, mimiking FH-II phenotype demonstrating that pharmacotherapy may be effective. This also implies that FH-II/III should be considered in the differential diagnosis of hypertensive children and, perhaps, that the offspring of patients with hyperaldosteronism should be screened for hypertension.