A subsyndromal risk factor study evaluated ICSDC nursing assessment data for 100 consecutive mechanically ventilated patients admitted to the ICU at Tufts MC for ≥ 24 hours without a neurologic reason for admission (e.g., acute stroke) or having acute alcohol withdrawal. Of the 100 patients, 72 developed subsyndromal delirium (ICDSC 1 to 3). Of these 72 patients, 26 (36%) went on to develop delirium (ICDSC ≥ 4) during their ICU admission. The remaining 28 patients developed neither subsyndromal delirium or delirium over the course of their ICU stay. For the 26 patients who developed delirium, we found that only 2 of the patients received ≥ 1 dose of haloperidol therapy in the period prior to when delirium was first identified. In contrast, for the 46 patients with subsyndromal delirium who did not progress to delirium, 14 of these patients received ≥ 1 dose of haloperidol during their ICU stay. Therefore, there was a weak association for a lower incidence of delirium in those patients with subsyndromal delirium who received ≥ 1 dose of haloperidol at any time during their ICU admission than patients who did not receive haloperidol [2/16 (12.5%) vs 24/56 (43%), p < 0.0001]. This retrospective, observational data suggests that patients with subsyndromal delirium who are exposed to haloperidol may remain in subsyndromal delirium and not progress to delirium. However, there are many methodological limitations with this pilot study thus it remains unknown if administering low-dose haloperidol to ICU patients with subsyndromal delirium will prevent the development of delirium.