Percutaneous fine-needle aspiration biopsy of solid adrenal masses was performed under real-time sonographic guidance in 18 patients. Cellular material was aspirated in all cases. Cytologic examinations were correct in 11 metastatic deposits, three primary adrenal adenocarcinomas, and one pheochromocytoma. One subsequently proven primary adenocarcinoma was not diagnosed. In two cases of adenoma, normal adrenal cells were aspirated. Percutaneous aspiration of adrenal masses is recommended when the precise nature of the lesions is clinically required. The simplicity and speed of fine-needle aspiration biopsy under sonographic control and its high diagnostic accuracy and safety suggest its use as a routine procedure in the management of patients with adrenal masses well depicted by sonography.