Primary aldosteronism (PA) is caused by an adrenal aldosterone-producing tumor (A-APT) or adrenal hyperplasia. An extra-adrenal APT (E-APT) as a cause of PA has been reported in 5 cases. Autopsy studies show a high incidence of ectopic adrenocortical tissue. We did a prospective study of the prevalence of A-APTs and E-APTs and the biochemical features of E-APTs in patients with PA.