A total of 98 adrenal glands in 49 patients were prospectively investigated by ultrasonography (US). The US had a sensitivity of 76.7%, a specificity of 92.7%, and an accuracy of 85.7%. It is mainly the smaller lesions (0.5 to 2.8 cm, mean 1.2) which decrease the sensitivity of US. Large tumors in or near the glands and anatomical variants may decrease the accuracy of US as well. The ultrasound detection of a large and solid adrenal tumor, especially one with irregular border, or a tumor with invasion to the inferior vena cava, suggests the high possibility of malignancy. While a tumor with central necrosis may be suggestive of pheochromocytoma, despite its large size. US is a good primary screening modality for patients with suspected adrenal lesions; and it may help to differentiate malignant from benign tumors of the adrenal.