Background and purpose — Day-case hip and knee arthroplasty has gained in popularity, but there are conflict-ing results regarding readmissions. We aimed to investigate differences in 30-and 90-day readmission rates between day-case patients and patients with a single overnight stay following primary total hip arthroplasty (THA), total knee arthroplasty (TKA), and unicompartmental knee arthro-plasty (UKA). Patients and methods — We identified day-case (DC) and overnight (ON) THA, TKA, and UKA patients, oper-ated on between 2010 and 2020, from the Danish National Patient Register. Day-case surgery was defined as discharge on the day of surgery. Overnight readmissions within 30 or 90 days of surgery were considered readmissions. We compared readmission rates between DC and ON patients within arthroplasty types using logistic regression adjusted for patient characteristics and year of surgery. We included 29,486 THAs (1,353 DC and 28,133 ON), 15,116 TKAs (617 DC and 14,499 ON), and 6,440 UKAs (1,528 DC and 4,914 ON). Results — The 30-day readmission rates were: DC-THA 4.4% vs. ON-THA 4.4% (adjusted odds-ratio [aOR] 1.2, 95% confidence interval [CI] 0.91–1.6), DC-TKA 4.7% vs. ON-TKA 4.4% (aOR 1.1, CI 0.69–1.5), and DC-UKA 3.0% vs. ON-UKA 3.0% (aOR 1.1, CI 0.78–1.5). Similarly, no sig-nificant differences were present between DC and ON THA, TKA, and UKA regarding 90-day readmissions or time to readmission. Conclusion — We found no differences in readmission rates between day-case THA, TKA, and UKA patients and patients with a single overnight stay.