Abstract We conducted a retrospective review of 3218 primary total knee arthroplasties (TKA) performed over two years at an urban academic hospital network using clinical and administrative data. Increased length of stay (LOS) was associated with readmission (P<0.001). Readmission was not associated with age (P=0.100), gender (P=0.608), body mass index (P=0.329), or staged bilateral procedures (P=0.420). The most common readmitting diagnoses were post-operative infection (22.5%), hematoma (10.1%), pulmonary embolus (7.9%) and deep vein thrombosis (5.6%). Of readmissions, 53.9% were for surgical reasons and 46.1% were for medical reasons. Certain interventions described in previous literature may be more successful in minimizing unplanned readmissions by focusing on patients with extended LOS, elevated infection risk and low socioeconomic status.