Hospitalization can negatively affect mobility among older adults. Early detection of older patients most at risk for mobility decline can lead to early intervention and prevention of mobility loss. This study’s purpose was to identify factors from the International Classification of Functioning, Disability, and Health associated with mobility decline among hospitalized elders. We conducted a secondary analysis of data from 959 hospitalized adults age 65 and older. We estimated the effects of health conditions and environmental and personal factors on mobility decline using logistic regression. Almost half of the sample declined in mobility function during hospitalization. Younger age, longer length of hospital stay, having a hearing impairment, and non-emergency admit type were associated with mobility decline, after adjusting for covariates. Findings may be used to develop an evidence-based, risk-determination tool for hospitalized elders. Future research should focus on individual, environmental, and policy-based interventions promoting physical activity in the hospital.