Hospital readmission is a metric of hospital quality of care, yet little is known what factors predict hospital readmission following arthroplasty. Our aim was to identify variables associated with early readmission following knee and hip arthroplasty, with focus upon hospital acquired conditions (HACs). Retrospective cohort analysis using Surgical Care Improvement Project (SCIP) and Veteran's Affairs Surgical Quality Improvement Program (VASQIP) data was performed over a five-year period. Following 26,710 total and partial primary arthroplasties (16,808 knees and 9902 hips), the overall 30-day readmission was 7.3% (1940) with readmission rates of 6.6% for knee arthroplasty and 8.4% for hip arthroplasty. HACs accounted for 42% of all complications and were the strongest predictor of readmission. Efforts to reduce these events may improve cost and safety of arthroplasty.