Objectives: Examine the effects of postacute discharge setting on unplanned hospital readmissions following total knee arthroplasty (TKA) in older adults. Design: Secondary analyses of 100% Medicare (inpatient) claims files. Setting: Acute hospitals across the United States. Participants: Medicare fee-for-service beneficiaries >= 66 years of age who were discharged from an acute hospital following TKA in 2009-2011 (n = 608,031). Measurements: The outcome measure was unplanned readmissions at 30, 60, and 90 days. The independent variable of interest was postacute discharge setting: inpatient rehabilitation facility (IRF), skilled nursing facility (SNF), or community. Covariates included demographic, clinical, and facility-level factors. The top 10 reasons for readmission were tabulated for each discharge setting across the 3 consecutive 30-day time periods. Results: A total of 32,226 patients (5.3%) were re-admitted within 30 days. Compared with community discharge, patients discharged to IRF and SNF had 44% and 40% higher odds of 30-day readmission, respectively. IRF and SNF discharge settings were also associated with 48% and 45% higher odds of 90-day readmission, respectively, compared with community discharge. The largest increase in readmission rates occurred within the first 30 days of hospital discharge for each discharge setting. From 1 to 30 days, postoperative and post-traumatic infections were among the top causes for readmission in all 3 discharge settings. From 31 to 60 days, postoperative or traumatic infections remained in the top 5-7 reasons for readmission in all settings, but they were not in the top 10 at 61 to 90 days. Conclusions: Patients discharged to either SNF or IRF, in comparison with those discharged to the community, had greater likelihood of readmission within 30 and 90 days. The reasons for readmission were relatively consistent across discharge settings and time periods. These findings provide new information relevant to the delivery of postacute care to older adults following TKA. (C) 2017 AMDA - The Society for Post-Acute and Long-Term Care Medicine.