Objective: To evaluate the diagnostic efficacy of CT indifferentiating adrenal adenomas from malignant tumors. Methods: 124 patients with 147 adrenal adenomas and malignant tumors were analyzed. Tumor size, margin, internal structure and the relation of the tumor to the adrenal gland were investigated with CT. Both precontrast and postcontrast CT attenuation values of the tumor were measured and the enhanced degree was calculated respectively. CT pixel mapping of the tumor was done in 20 patients. Results were analyzed by using ROC curve. Results: The area under the ROC curve for precontrast CT attenuation values (0.91± 0.05) was significantly larger than that for postcontrast CT attenuation values (0.83± 0.04), enhanced degree (0.74± 0.08) or tumor sizes (0.82± 0.04). With a threshold of tumor size 3.0 cm, homogenous density, precontrast CT attenuation value 20 HU, postcontrast CT attenuation value 35 HU or enhanced degree 20 HU, the sensitive for characterizing adenomas were 86%, 85%, 88%, 76% and 74%, and the specificity were 73%, 72%, 91%, 78% and 61% respectively. Connection with normal adrenal gland (68%), precontrast CT attenuation value