The safety and efficacy of treating ICU patients with delirium symptoms with antipsychotic therapy has not been evaluated. Recent data highlights the deleterious sequelae of subsyndromal delirium in the ICU. In addition, the results of two studies demonstrate the benefits of administering low-dose antipsychotic therapy in patients at high risk for delirium. We therefore hypothesize that treatment of subsyndromal delirium in the critically ill with haloperidol will prevent progression to clinical delirium. This should be associated with decreased agitation, a shorter duration of mechanical ventilation, and improved cognitive function after ICU discharge. Given the documented safety of low-dose haloperidol therapy in clinical practice, we anticipate the potential risk-benefit ratio for this intervention to be low - particularly in an ICU environment where patients receive continuous cardio- respiratory monitoring.