Adrenal tumors are being detected more frequently in consequence of the wider application of increasingly sensitive radiological investigation techniques. According to the working hypothesis that more silent adenomas could develop from hyperplastic tissue areas under increased stimulation of the adrenal cortex, heterozygous and homozygous patients with congenital adrenal hyperplasia (CAH) were studied. A high incidence of adrenal masses, nearly 82% in homozygous and 45% in heterozygous patients, was found. There was no correlation between tumor size and serum 17-hydroxyprogesterone concentrations. These tumors are, therefore, probably silent adenomas. On the basis of these results, CAH should always be ruled out in the case of incidentally detected adrenal masses. Since CAH is a relatively frequent disease, and the adrenal carcinoma belongs to the rarest malignant tumors, a malignant transformation of these tumors seems to be unlikely.