Background: This study examines effects of mobility and cognition on hospitalization and inpatient days among women late in life. Methods: Prospective study of 663 women (mean age 87.7 years) participating in the Study of Osteoporotic Fractures Year 20 examination (2006-2008) linked with their inpatient claims data. At Year 20, mobility ascertained by Short Physical Performance Battery categorized as poor, intermediate, or good. Cognitive status adjudicated based on neuropsychological tests and classified as normal, mild cognitive impairment, or dementia. Hospitalizations (n = 182) during 12 months following Year 20. Results: Reduced mobility and poorer cognition were each associated in a graded manner with higher inpatient health care utilization, even after accounting for each other and traditional prognostic indicators. For example, adjusted mean inpatient days per year were 0.94 (95% confidence interval [CI] 0.52-1.45) among women with good mobility increasing to 2.80 (95% CI 1.64-3.89) among women with poor mobility and 1.59 (95% CI 1.08-2.03) among women with normal cognition increasing to 2.53 (95% CI 1.55-3.40) among women with dementia. Women with poor mobility/dementia had a nearly sixfold increase in mean inpatient days per year (4.83, 95% CI 2.73-8.54) compared with women with good mobility/normal cognition (0.84, 95% CI 0.49-1.44). Conclusions: Among women late in life, mobility limitations and cognitive deficits were each independent predictors of higher inpatient health care utilization even after considering each other and conventional predictors. Additive effects of reduced mobility and poorer cognition may be important to consider in medical decision making and health care policy planning for the growing population of adults aged >/=85 years.