Primary aldosteronism remains a diagnostic challenge. Certain immunoassay techniques, simplified diagnostic testing, and the introduction of sensitive imaging techniques have facilitated the diagnosis, but obstacles that remain include a lack of optimal screening methods, low sensitivity and specificity of current diagnostic tests, and a growing number of etiological subgroups. A rational approach to the diagnosis of primary aldosteronism is described, as is the differentiation of the surgically correctable lesion (adenoma) from the other etiological subgroups.