Numerous studies have explored 90-day readmissions following total joint arthroplasty; however, there is a paucity of literature concerning 90-day emergency department (ED) visits. The authors aimed to characterize the risk factors for ED presentations and to determine the primary reasons for return, hypothesizing that certain medical comorbidities would account for resource utilization. The institutional database was queried for primary total hip arthroplasty (THA) and total knee arthroplasty (TKA). Patients were stratified based on return visits to the ED within 90 days postoperatively. Univariable and multivariable analyses were performed to determine the factors most predictive of ED return for each THA and TKA. A total of 10,479 procedures resulted in 1234 90-day ED visits made by 937 patients. Significant predictors of 90-day ED return after THA included black race, age older than 80 years, congestive heart failure, valvular heart disease, metastatic disease, peripheral vascular disease, alcoholism, drug use, depression, and discharge to a skilled nursing facility. In contrast, only black race, liver insufficiency, cancer, and pulmonary hypertension were predictive of ED return following TKA. The primary risk factors for ED return differ for THA and TKA, and this is not currently reflected in the medical severity diagnosis-related group system. Specifically, black patients with multiple comorbidities are at high risk for unplanned ED visits following THA. This should be considered in patient counseling and outreach programs when attempting to mitigate the postoperative risks and to decrease 90-day resource utilization in this patient population. [Orthopedics. 2020;43(5):295-302.].