Aspiration pneumonia is a serious problem for the elderly institutionalized person, often requiring transfer to a hospital and a lengthy stay there. It is associated with a high mortality rate and is very costly to the health care system. The current study sought to determine the key predictors of aspiration pneumonia in a nursing home population with the hope that health care providers could identify those residents at highest risk and focus more efforts on prevention of this serious disease. A cross-sectional, retrospective analysis was done, using the Minimum Data Set (MDS) nursing home assessment data for three states (New York, Mississippi, Maine) from 1993 to 1994 (N = 102842). Nursing home residents were aged 65+. Standardized MDS summary scales and their component items were used, including: the Activities of Daily Living (ADL) scale, the cognitive performance scale (CPS), and the Resource Utilization Groups (RUGs). Results of these analyses showed the prevalence of pneumonia among this population was 3% (n = 3118). Results from the logistic regression models indicated 18 significant predictors of aspiration pneumonia. The strongest to weakest predictors of pneumonia were, respectively, suctioning use, COPD, CHF, presence of feeding tube, bedfast, high case mix index, delirium, weight loss, swallowing problems, urinary tract infections, mechanically altered diet, dependence for eating, bed mobility, locomotion, number of medications, and age, while both CVA and tracheotomy care were inversely predictive of pneumonia. The emergence of these significant predictors suggested a different pathogenesis of pneumonia in the elderly nursing home resident from the acute care patient or the outpatient. Nursing home residents have chronic medical conditions that gradually lead to "decompensation" in functional status, nutritional status, and pulmonary clearance. Dysphagia and aspiration are common complications of their medical conditions and may slowly worsen as their status deteriorates. Alternatively, a sudden adverse event may dramatically increase the amount aspirated or the ability to resist infection and lead to sudden decompensation. Clinical staff must identify residents with dysphagia and aspiration and work to prevent decline in functional status in all residents. They must be aware of the dangers of adverse events that lead to sudden inactivity or illness and increase the risk of aspiration pneumonia. Prevention of this disease whenever possible will reduce costs, improve health outcomes, and improve our quality of care.