Primary Aldosteronism (PA) is a disease caused by the overproduction of aldosterone hormone from the adrenal glands. PA causes hypertension and the majority with this disease are undiagnosed for PA. There are new insights into this matter by using biochemistry as well as advanced radiology. In 2011, a breakthrough in the genetic derangements came, identifying a mutated potassium channel gene – KCNJ5 – in about 40% of PA with adenoma. Chapters in this book include a history of the disorder, epidemiology, genetics derangements, the KCNJ5 mutations and phenotype and more.