Background: Previous research on risk of delirium in acute hospital settings identified mainly patient variables (e.g., age) that are not amenable to intervention. The purpose of this study was to develop a model for new delirium in hospitalized older patients that included process of care and social variables. Methods: A prospective cohort study was undertaken in a community hospital in Ontario, Canada. Research paticipants included 156 hospitalized patients age 65+ years and without delirium on admission who were admitted to a medical or surgical unit. The measures included daily appraisal of delirium using a standardized and validated tool, and assessment of patient, process of care, and social variables. Results: Delirium developed in 28 of the 156 patients (17.9%). Older age and cognitive impairment were significant patient variables. Significant process of care variables included a high number of medications administered during hospitalization, surgery, a high number of procedures during early hospitalization (e.g., x-rays, blood tests), and intensive care treatment. Conclusions: Approximately one older patient in five developed delirium after admission to a medical or surgical unit. Risks not easily amenable to intervention included age, cognitive dysfunction, surgery, and intensive care requirements. Risk factors that are potentially modifiable included number of medications and number of procedures. Future research might focus on the efficacy of such intervention to reduce new-onset delirium in acute hospital settings.