PURPOSE:Although its defining feature is the development of multiple large‐bowel polyps, familial adenomatous polyposis is a generalized disorder of tissue growth regulation, with a range of manifestations. An association between adrenal neoplasms and familial adenomatous polyposis has been suggested, but not prospectively documented. Patients with familial adenomatous polyposis were therefore screened to determine the frequency of adrenal masses.METHODS:Patients with familial adenomatous polyposis underwent spiral abdominal CT scan reported by two radiologists specialized in cross‐sectional imaging.RESULTS:One hundred seven individuals were examined (median age, 36 (interquartile range, 30‐48) years; 57 male). Fourteen (13 percent) had an adrenal mass of 1 cm or greater (bilateral in one case); none had clinical evidence of endocrine disturbance or hypertension. Two lesions were histologically confirmed adrenocortical adenomas and one a phaeochromocytoma; the remaining 12 had CT appearances of nonhyperfunctioning adrenocortical adenoma.CONCLUSIONS:The prevalence of unsuspected adrenal masses in the general population is approximately three percent. This prospective study found a significantly higher frequency of 13 percent in patients with familial adenomatous polyposis (chi‐squared=6.973; df=1;P=0.008). There is no evidence that the histologic nature of these differs from that in the general population.