The purpose of this study is to determine whether chin-down posture or use of a thickened liquid diet is more effective in the prevention of aspiration and aspiration pneumonia in patients with Parkinson's disease and/or dementia. Liquid aspiration is the most common type of aspiration in older populations, especially those suffering from debilitation, dementia, and depression. Pneumonia may develop as a consequence of aspiration and is the fifth leading cause of death in the US among persons age 65 years and over. Current treatment involves either use of chin-down position with swallowing or use of thickened liquids in the diet, without any clear evidence supporting the use of one treatment over the other. This is a Phase III inpatient and/or outpatient study in which all participants will be randomly assigned to either the chin-down position or the thickened liquid treatment group based on swallowing function during a modified barium swallow. This study is scheduled to recruit patients for a three-year period; participation by each individual patient spans no more than three months after entry.