With the increasing use of abdominal cross-sectional imaging in the investigation of patient symptoms and in cancer staging, incidental adrenal masses are frequently detected. The most common clinical question is whether these masses are benign or malignant. Benign adrenal masses such as myelolipomas, lipid-rich adenomas, adrenal cysts and adrenal haemorrhage have pathognomonic imaging findings. However, there remains a significant overlap between the imaging appearances of some lipid-poor adenomas and malignant lesions, particularly metastases and small adrenal carcinomas. Our review looks at the recent advances in computed tomography, magnetic resonance imaging and positron emission tomography, which can be used to assist in the distinction between benign adenomas and malignant lesions of the adrenal gland.