Acute adrenocortical insufficiency is an unusual cause of isolated shock. The purpose of this study is to describe the cardiovascular changes in 6 patients with acute adrenal insufficiency presenting with hemodynamic instability.Retrospective and prospective study.Medical intensive care unit in a university hospital.6 patients studied by right cardiac catheterization.Results before glucocorticoid treatment show two possible hemodynamic states: 1) myocardial depression with hypovolemia in 3 patients, and 2) hyperdynamic shock with high cardiac output and diminished systemic arterial resistance in 3 other patients. The 3 patients presenting hyperdynamic shock were all given intravenous fluid therapy of over 20 ml/kg before the first hemodynamic measurement. For 2 other patients with low cardiac index and high systemic arterial resistance studied prospectively, 20 ml/kg intravenous fluid therapy transformed the hemodynamic state to hyperdynamic shock. The cardiovascular effect of glucocorticoid treatment studied in 4 patients was resulted in an improvement in the left ventricular systolic work index.Diagnosis of acute adrenocortical insufficiency must be considered if clinical manifestations are present suggesting septic shock without any obvious infectious cause in patients having undergone considerable intravenous fluid therapy as an initial course of treatment.