['To identify the relationship between functional status and complicated clinical course in older adults in the emergency department (ED) with suspected infection and to identify other independent predictors of complicated clinical course.', 'A prospective observational cohort study.', 'An academic, tertiary care ED with 70,000 visits per year.', 'Aged 65 and older, blood cultures obtained in the ED, and final ED physician diagnosis of acute infection.', 'Functional status was obtained using the Older Americans Resources Scale (OARS). Complicated clinical course was defined as in-hospital mortality, need for intensive care unit (ICU)-level care, or worsening in sepsis criteria within 48\xa0hours. Analysis was performed using multivariable logistic regression.', 'One hundred five participants were enrolled, 34 with the primary outcome. OARS was not predictive of complicated clinical course in univariate (P\xa0=\xa0.13) or multivariable (P\xa0=\xa0.90) models. An OARS score of 25 or less was also not significant (P\xa0=\xa0.22). Independent predictors were immunosuppression (odds ratio (OR)\xa0=\xa03.45, 95% confidence interval (CI)\xa0=\xa01.06-11.20), systolic blood pressure (OR\xa0=\xa00.98, 95% CI\xa0=\xa00.96-1.00), pulse (OR\xa0= 1.03, 95% CI\xa0=\xa01.00-1.06), metabolic acidosis (OR\xa0=\xa03.46, 95% CI\xa0=\xa01.08-11.09), severe sepsis or septic shock (OR\xa0=\xa010.24, 95% CI\xa0=\xa01.44-72.79), and suspected bloodstream infection (OR\xa0=\xa03.56, 95% CI\xa0=\xa01.13-11.16).'] Does functional status predict complicated clinical course in older adults in the emergency department with infection?