ObjectivesTo determine the clinical variables that affect the prognosis of critically ill patients with sustained unexplained hypotension. A further goal was to develop a prognostic scoring system based on clinical data available at the onset of hypotension.DesignProspective cohort study.SettingThe intensive care units (ICUs) of an academic medical center.Patients60 mins) unexplained hypotension. Using the initial 50 patients (derivation set), a prognostic score was developed that was then tested in the next 51 patients (validation set).InterventionsNone.Measurements and Main Resultsor=to65, mortality 92%, (n = 24). The area under the receiver operating characteristic curve was .85 for the derivation set and .83 for the validation set vs. .76 for the APACHE II score alone.ConclusionsThe prognosis of hypotension in the critical care setting is highly variable, but can be predicted from patient characteristics.(Crit Care Med 1996; 24:1835-1840)