We reviewed the value of computerized tomography (CT) in the preoperative evaluation of 34 patients with primary aldosteronism. All 34 patients entered a standard protocol including saline suppression testing, abdominal CT scanning, and adrenal venous sampling. Surgical pathologic findings, biochemical determinations, and clinical response to adrenalectomy were the criteria used to evaluate 68 adrenals in 34 patients. Of 36 diseased glands 17 were correctly identified by CT (48%). Of the 32 normal glands, 29 were identified correctly by CT (91%). Thus, CT is not sensitive (0.48), but very specific (0.91) in Conn's syndrome. Our patients were divided into two groups: group 1 were those scanned between 1977 and 1980, group 2 were those scanned from 1981 to 1983 with a high-resolution GE-8800 scanner. CT results in group 2 showed no significant improvement in specificity (0.92), but improvement in sensitivity (0.58) over group 1 (specificity 0.90, sensitivity 0.42). Furthermore, CT is less sensitive in patients with smaller tumors than in those with larger tumors.