<i>Background:</i>Through the widespread use of imaging techniques with great sensitivity, adrenal tumours are often diagnosed as an incidental finding. The majority of these adrenal lesions are benign and without evidence of endocrine activity or malignancy. However, in addition to the classic forms of overt adrenal hypersecretion, it has become evident in recent years that even modest adrenal hormonal autonomy, as exhibited in clinically silent phaeochromocytoma, normokalaemic primary aldosteronism and subclinical Cushing syndrome, is associated with significant morbidity. Thus, hormone hypersecretion and growth kinetics must be ruled out for each patient using specific tests to avoid associated morbidity. <i>Conclusions:</i>Detection and differential diagnosis of subtle changes in adrenal hormone secretion can pose a diagnostic challenge to the clinician, and accurate diagnosis is dependent on use of tests with reliable sensitivity and specificity.