The rapid cosyntropin stimulation test offers a simple means for detecting adrenal insufficiency. In contrast, assessment of suspected hypercortisolism (Cushing's syndrome) is difficult because cortisol levels fluctuate with intermittent release of corticotropin from the pituitary or from tumors. Also, a number of medications affect cortisol levels, leading to false-positive or false-negative results. The classic low-dose followed by high-dose dexamethasone test is cumbersome, and other, simpler studies, such as the overnight high-dose dexamethasone suppression test, may prove more practical and cost-effective. With both high and low levels of adrenal glucocorticoids, awareness and early recognition of the symptoms are important. An endocrinologist should be consulted when the overnight dexamethasone suppression test or the 24-hour urine cortisol collection is abnormal or if clinical suspicion is high despite normal results on screening tests.