Background: Adrenocortical dysfunction is unusual in the unselected critically ill patient, Case reports document a state of corticosteroid responsive vasopressor dependence, resembling the systemic inflammatory response syndrome, The exact incidence of this disorder is unknown. Methods: We prospectively studied the incidence of adrenal insufficiency during a 9-month period in a surgical intensive care unit (ICU) population, Trauma, general surgery, urology, and gynecologic-oncology patients were included, Patients who met criteria were given a cosyntropin stimulation test. Results: Overall, the incidence of adrenal insufficiency was 0.66%, In the subgroup of patients with greater than 14 days stay in the ICU, 6% were found to have adrenal insufficiency, In patients aged more than 55 years and with ICU stays of 14 days or greater, 11% were adrenally insufficient. Conclusions: Screening of critically ill patients for adrenal insufficiency, particularly those with prolonged ICU stay and age greater than 55 years, is warranted.