Over a 2 year period, 63 of 1,459 patients examined by computerized tomography were found to have adrenal masses. In 19 patients (1.3 percent of patients examined and 30 percent of patients with adrenal masses), they were unexpected and did not give rise to symptoms or signs. Three patients were explored. Two of the patients had adrenocortical adenomas and a third, a ganglioneuroma. Adrenal function tests were performed in 14 patients and showed evidence of Cushing's syndrome in 1 patients and revealed no abnormalities in 13. The lesions in 10 of 11 nonsurgical patients followed by computerized tomography for 11 to 36 months showed no change. One lesion became significantly smaller. In a review of 988 autopsy reports, grossly visible adrenal masses were present in 73 patients (7.3 percent), including 19 adrenocortical adenomas (1.9 percent) and 50 metastases (5 percent). We conclude that serendipitous adrenal masses are usually small, nonfunctioning, and benign, the most common lesion being adrenocortical adenoma. A protocol has been suggested for management to identify the minority of patients with functioning or malignant lesions and to avoid unnecessary surgery in the others who have benign disease.