Glucocorticoid-remediable aldosteronism (GRA) is a rare form of inherited hypertension caused by a characteristic gene duplication. With the advent of definitive genetic testing for GRA, the performance of the traditional screening test for GRA, the dexamethasone suppression test (DST), can be evaluated. We compared the DST to direct genetic testing in 24 patients referred for genetic screening for GRA (12 GRA positive and 12 GRA negative) based on clinical and biochemical findings, DST, and family history. Plasma aldosterone was measured before and after oral dexamethasone administration to determine the extent to which aldosterone was suppressed by glucocorticoids in each patient group. The results of the DST in these subjects were also compared to those in 19 historical patients with primary aldosteronism 4 bilateral hyperplasia and 15 aldosterone-producing adenoma (APA) reported previously. The DST differentiated GRA-positive from GRA-negative patients with 92% sensitivity and 100% specificity. Cutoffs based on the post-DST plasma aldosterone level (< 4 ng/dL) or percent suppression compared to baseline (> 80%) were equally effective in correctly diagnosing GRA (only one GRA-positive patient would have been incorrectly diagnosed). However, DST in 15 APA patients revealed that 33% had greater than 80% suppression of aldosterone, and 1 had aldosterone levels below 4 ng/dL. We conclued that a post-DST aldosterone level below 4 ng/dL will correctly diagnose GRA patients with high sensitivity and specificity. Suppression compared to baseline can be misleading, as evidenced by the results in APA patients and referred subjects who genetically screened negative.