Objective To evaluate the clinical, endocrinologieal and pathological characteristics of adrenal incidentaloma. Methods Ninety-seven patients (53 males and 44 females) diagnosed with adrenal incidentaloma confirmed by pathology were retrospectively analyzed in this study. The mean patient age was 45 years old. Thirty-eight cases had left adrenal lesions, 52 cases had right adrenal le-sions and 7 cases had bilateral adrenal tumors. Of these patients, 74 cases had accepted full range en-docrinological investigations. The tumor size was measured by uhrasonography (US) in 8 cases, CT scanning in 54 cases and MRI in 35 cases, respectively. Results Of these 97 adrenal incidentalomas, 20 cases(20.6%) were malignant tumors (12 adrenoeortical carcinomas, 3 malignant pheochromocyto-mas, 2 metastatic cancers, 1 sarcoma, 1 neuroblastoma and 1 malignant sehwannoma), 21 cases (21.6%) were benign pheochromocytomas, 26 cases (26.8%7 were adrenal adenomas, 9 cases (9.3%) were myelolipomas,13 cases(13.4%) were adrenal cysts, 5 cases(5.2%) were ganglioneuro-ma and 3 cases(3.1%) were neurofibroma. Endoerinological study showed that 21 (28. 4%) of the in-cidentalomas were functional. Forty patients(41.2%) had hypertension. Tumor size less than 4 cm in diameter were found in 25.8%cases,tumor size ranged from 4 to 6 em were found in 34.0% cases and tumors larger than 6 em were found in 40.2% cases. The average diameter of malignant tumors was 9.9±4.6 cm which was significantly larger than the average diameter of benign tumors, 5.6±3.2 cm (P=0.01). Tumor size greater than 6 cm was more frequently found in patients with malignant tumor (75.0% vs 35.1%, P=0.001). Only 4% of the ineidentalomas less than 4 cm selected surgery were malignant tumors. Weight loss was more frequently found in patients with malignant tumor than that in benign tunor(25.0% vs 2.6%, P =0.004). Conclusions Adrenal adenomas, benign pheochro- mocytomas and malignant tumors are the main types of adrenal incidentaloma. The endocrinological evaluation should be performed in all adrenal incidentalomas. In patients with normal endoerinologieal study, tumor size less than 4 cm is an important eharaeteristie for benign tumors.