Dexamethasone suppression [Iodine-131] 6-Beta-Iodomethy1-19- Norcholesterol (I-131 NP-59) adrenal cortical scintigraphy was performed in 35 patients with suspected primary aldosteronsim, between May 1983 and June 1990. Based on clinical, biochemical, radiographic and pathologic data, the diagnostic accuracy of primary aldosteronism from I-131 NP-59 adrenal cortical scintigraphy was evaluated. The sensitivity, specificity, positive predictive accuracy and negative predictive accuracy was 78.9%, 100%, 100% and 80% respectively. We conclude that I-131 NP-59 adrenal cortical scintigraphy is an accurate and noninvasive technique for the diagnosis of suspected primary aldosteronism.