Asymptomatic adrenal masses - incidentalomas - have become a common clinical and diagnostic problem with increasing prevalence, mainly due to advances in abdominal imaging technology. The prevalence of these lesions increases with age, and an appropriate diagnostic work-up is a growing challenge in our ageing society. Unsuspected adrenal masses are detected in up to 5% of abdominal imaging procedures, and the limited availability of studies on incidence, prevalence and natural development complicates the decision regarding diagnostic work-up. The majority of asymptomatic adrenal masses are non-hyperfunctioning adenomas. However, there are a large number of entities also appearing as non-functioning adrenal lesions. While each type of incidentally found non-adenomas is itself rare, altogether they represent a substantial amount. Most of these lesions do not have specific imaging features. Nevertheless, radiological evaluation usually allows narrowing of the differential diagnosis. Magnetic Resonance Imaging (MRI) is considered an excellent tool in the differentiation between adenomatous and non-adenomatous adrenal masses. Even in cases which are indeterminate on CT, the nature of the adrenal lesion can often be determined using MRI. Chapter Adrenal incidentalomas is a full review of state of the art in imaging and diagnosis of adrenal lesions, which could appear as incidentalomas of the adrenal glands. Different competitive imaging methods are discussed and compared, with focus on MRI techniques and a comprehensive description of the epidemiology and pathophysiology of adrenal lesions is given.