Purpose: This study was designed to identify which of 3 treatments for aspiration on thin liquids--chin-down posture, nectar-thickened liquids, or honey-thickened liquids--results in the most successful immediate elimination of aspiration on thin liquids during the videofluorographic swallow study in patients with dementia and/or Parkinson's disease. Method: This randomized clinical trial included 711 patients ages 50 to 95 years who aspirated on thin liquids as assessed videofluorographically. All patients received all 3 interventions in a randomly assigned order during the videofluorographic swallow study. Results: Immediate elimination of aspiration on thin liquids occurred most often with honey-thickened liquids for patients in each diagnostic category, followed by nectar-thickened liquids and chin-down posture. Patients with most severe dementia exhibited least effectiveness on all interventions. Patient preference was best for chin-down posture followed closely by nectar-thickened liquids. Conclusion: To identify best short-term intervention to prevent aspiration of thin liquid in patients with dementia and/or Parkinson's disease, a videofluorographic swallow assessment is needed. Evidence-based practice requires taking patient preference into account when designing a dysphagic patient's management plan. The longer-term impact of short-term prevention of aspiration requires further study.