Clinically silent adrenal masses discovered by imaging studies performed for unrelated reasons, i.e. adrenal incidentalomas, have become a rather common finding in clinical practice. However, only limited studies of incidence, prevalence, and natural history of adrenal incidentalomas are available. A comprehensive review of the literature shows the prevalence of adrenal incidentalomas to be 2.3% at autopsy and 0.5-2% at abdominal computed tomography scan. Most lesions are adrenocortical adenomas at histology, whereas the prevalence of adrenocortical carcinomas is relatively low. The risk of malignancy over time for masses defined as benign at diagnosis is estimated at about 1/1000, even though 5-25% of masses increase in size during follow-up. Hyperfunction develops in about 1.7% of cases and the risk is higher in patients with lesions larger than 3 cm. Cortisol hypersecretion is the most likely disorder that may ensue, and it remains subclinical in about two-thirds of cases. The lack of controlled studies precludes making specific management recommendations. Large perspective controlled studies to define the epidemiology, natural history, and possible associated morbidity of adrenal incidentalomas and their impact on the quality of life of patients are needed.