Hospital readmissions pose negative health risks for older adults and reflect low quality, high cost healthcare. Efforts to reduce readmissions have focused on disease-specific interventions that target patients during the transition from the hospital or in the post-acute care setting. Less attention has spotlighted the role of hospital nursing. Staff nurses represent an around-the-clock surveillance system that is well-positioned to recognize patients' physical and social needs that may contribute to a readmission. This cross-sectional secondary data analysis explored the association between the working conditions of hospital nurses - staffing and the practice environment - and 30 day readmissions among older adults following elective total hip and total knee arthroplasty. Data sources from 2005-2006 included patient administrative data, nurse survey data, and hospital organizational data. Nurse survey responses were aggregated to construct hospital measures of nurse staffing and the practice environment. The main outcome of interest was 30 day unplanned readmission. The analytic sample consisted of 112,018 Medicare patients electively undergoing either total hip or total knee arthroplasty, and 23,089 registered nurses working in 495 acute care hospitals in four states (CA, FL, NJ, PA). The sample was descriptively analyzed using cross-tabulations, Kaplan-Meier plots, and histograms. Multivariable logistic regressions estimated the effect of nurse staffing and the practice environment on 30 day readmission, adjusting for patient and hospital covariates and accounting for clustering of patients within hospitals. The 30 day unplanned readmission rate was 5.6% and 5.7% for hip and knee patients, respectively. After adjusting for patient and hospital covariates, each additional patient was associated with an 8% increase in the patient's likelihood of readmission. Patients cared for in a better practice environment, as compared to a mixed or poor environment, had 13% lower odds of readmission; however, this relationship became insignificant once adjusting for nurse staffing. These findings reveal that a substantial percentage of older adults experience an unplanned rehospitalization following elective total hip and total knee arthroplasty. The evidence suggests that improving nurse staffing and the practice environment may be strategies for reducing readmissions among older adult orthopedic surgical patients.