With the increasing use of abdominal cross-sectional imaging, incidental adrenal masses are frequently detected. The commonest clinical question is whether these are benign adenomas or malignant primary or secondary masses. The nature of incidentally detected adrenal masses can be determined with a high degree of accuracy using computed tomography (CT) and magnetic resonance imaging (MRI) as benign adrenal masses such as myelolipomas, lipid-rich adenomas, adrenal cysts and adrenal haemorrhage which have pathognomonic imaging findings. However, there remains a significant overlap between the imaging features of some lipid-poor adenomas and malignant lesions. We review the recent advances in CT, MRI and positron emission tomography (PET) which can be used to distinguish between benign adenomas and malignant lesions of the adrenal gland.