We retrospectively reviewed the imaging studies in 17 proved cases of primary aldosteronism to determine the value of the procedures used to detect adrenal tumors or adrenal hyperplasia. The procedures included CT with 3-, 5-, and/or 10-mm-thick sections (17 patients), 131I-6 beta-iodomethyl-19-norcholesterol (NP-59) scintigraphy (16 patients), and MR imaging (six patients). Proof of the adrenal abnormality was established in cases of tumor (seven adenomas, one carcinoma) by surgery and in cases of adrenal hyperplasia by surgery (three cases); venous sampling (three cases); or combined clinical, biochemical, and imaging data (three cases). Both CT and scintigraphy detected six of the seven adenomas and the adrenal carcinoma (88%). Regarding hyperplasia, CT was correct in five of six and scintigraphy was correct in two of four cases proved by surgery or venous sampling. CT and NP-59 were concordant and suggested the diagnosis of hyperplasia in the remaining three cases without surgical or venous sampling proof. MR detected both cases of adenoma in which it was performed and showed evidence of hyperplasia in one of the four cases of hyperplasia in which it was performed. Although the number of patients in this series is too small to have much statistical power, these results suggest that CT and NP-59 scintigraphy are equivalent in the detection of adrenal abnormalities in patients with primary aldosteronism. The value of MR in the detection of small adrenal contour abnormalities was limited by slice thickness capabilities.