Adrenal incidentalomas are clinically unsuspected lesions that are detected in adrenal glands during imaging procedures for other causes. With widespread use of imaging - both computed tomography (CT) and magnetic resonance imaging (MRI) - adrenal incidentalomas are now a common clinical problem. The two main clinical issues to be determined in this setting are the risk of malignancy and the hormonal activity of these lesions. The answers to these two questions, along with the clinical characteristics of each individual patient and co-morbidities, will guide the treatment strategy, which can vary from simple follow-up to surgical resection. The objective of this article is to present updated information on the definition, prevalence, imaging and functional features of adrenal incidentalomas and to provide a guide to their optimal assessment, treatment and follow-up. This review collected, analyzed and qualitatively re-synthesized information regarding: (1) the various clinical entities known as "adrenal incidentalomas", (2) the initial assessment of risk of malignancy, (3) the initial assessment of whether the lesion is hormonally active or non-functioning, (4) the absolute and relative indications for surgical treatment, (5) the follow-up of patients who are not deemed to need surgical treatment after initial assessment, and (6) the post-operative follow-up of patients who undergo surgical treatment. The evidence calls for clinicians to bear in mind the Hippocratian advice "ωϕελέειν ή μη βλάπτειν" ("first do no harm").