The risks of cognitive impairment among hospitalized patients over age 85 are not adequately understood. We used electronically recorded ICD-9 codes of inpatients over 85 years old to identify patients age > or =85 who showed signs of cognitive impairment during hospitalization at our institution. We randomly selected patient records showing cognitive impairment and patient control records matched for age and admission date but without cognitive impairment and obtained mortality information up to 18 months after discharge. Records were further examined to characterize hospital stay including reason for admission. After adjustment for comorbidities and potential confounders, patients over age 85 with ICD-9-defined cognitive impairment had increased risk of death within the hospital (hazard ratio (HR)=3.99; 95% confidence interval (CI) 0.42-37.90; p=0.229), in the first year after hospitalization (HR=2.35; 95% CI 1.15-4.78; p=0.019), and cumulatively (HR=2.46; 95% CI 1.26-4.82; p=0.009). In this matched cohort of hospitalized patients > or =85 years old, cognitive impairment was associated with an increased mortality rate. Because of this additional risk of death, hospitalized geriatric patients who are cognitively impaired may merit closer monitoring.