A retrospective study conducted from 1975-1987 at Vanderbilt University Medical Center and affiliated hospitals identified 28 patients, ranging in age from 22 to 74 years, who were noted to have "nonfunctioning" adrenocortical tumors. Eighteen (64%) were men, and ten (36%) were women. A left adrenal mass was present in 16 (57%) patients, a right in 11 (39%) patients, and one (4%) patient had bilateral adrenal enlargements. Nineteen patients underwent an adrenalectomy. Ten were found to have adrenocortical adenomas, ranging is size from 2.5-4.0 cm in greatest diameter. Three were adrenocortical carcinomas (3.0, 5.5, and 8.0 cm). A necrotic mass (14.0 cm) was found in one patient. Two patients had myelolipoma, one had ganglioneuroma, and one had a suspected primary melanoma. Five patients were not operated upon and were followed by serial computed tomographic scans for variable periods; two died of unrelated cardiac problems, and one was lost to follow-up. Three patients underwent biopsy with benign pathology. The data indicate a high incidence of adenoma and carcinoma in patients with nonfunctioning adrenal tumors that measure more than 3.0 cm in diameter. These tumors have the potential to progress to malignant degeneration without any recognizable clinical or endocrine abnormalities. The authors thus conclude that all patients with "nonfunctioning" adrenal tumors that are larger than 3.0 cm in diameter should undergo surgical exploration and excision.