Unplanned hospital returns after total joint arthroplasty (TJA) reduce any cost savings in a bundled reimbursement model. We examine the incidence, risk factors, and costs for unplanned emergency department (ED) visits and readmissions within 30 days of index TJA.We retrospectively reviewed a consecutive series of 655 TJAs (382 total knee arthroplasty and 273 total hip arthroplasty) performed between April 2014 and March 2015. Preoperative diagnosis was osteoarthritis of the hip or knee (97%) or avascular necrosis of the hip (3%). Hospital costs were recorded for each ED visit and readmission episode.Of the 655 TJAs reviewed, 55 (8.4%) returned to the hospital. Of these hospital returns, 35 patients (5.3%) returned for a total of 36 unplanned ED visits whereas the remaining 20 patients (3.1%) presented 22 readmissions within 30 days of index TJA. The 2 most common reasons for unplanned ED visits were postoperative pain/swelling (36%) and medication-related side effects (22%). Avascular necrosis of the hip was a significant risk factor for an unplanned ED visit (7.27 odds ratio [OR], 95% confidence interval [CI] 1.67-31.61, P = .008). Multiple logistic regression analysis revealed the following risk factors for readmission: body mass index (1.10 OR, 95% CI 1.02-1.78, P = .013), comorbidity >2 (2.07 OR, 95% CI 1.06-6.95, P = .037), and prior total knee arthroplasty (2.61 OR, 95% CI 1.01-6.72, P = .047). Ambulating on the day of surgery trended toward a lower risk for readmission (0.13 OR, 95% CI 0.02-1.10, P = .061). The 2 most common reasons for readmission were ileus (23%) and cellulitis (18%). The total cost associated with unplanned ED visits were $15,427 whereas costs of readmissions totaled $142,654.Unplanned ED visits and readmissions in the forthcoming bundled payments reimbursement model will reduce cost savings from rapid recovery protocols for TJA. Identifying and mitigating preventable causes of unplanned visits and readmissions will be critical to improving care and controlling costs.