Differences in in-hospital pain and consumption of opioids after primary total hip arthroplasty (THA) and knee arthroplasty (TKA) have been rarely studied in a setting where the patient course is otherwise similar. The aim of this study was to compare early pain intensity and opioid usage between patients who have undergone THA and TKA to identify potential implications for outpatient surgery.This institutional register study included 4655 patients receiving THA and 2675 patients receiving TKA. Pain at rest and during mobilization were collected once preoperatively, and postoperatively at five time-points, twice on the Day of surgery, once each on day 1 and day 2 after surgery, and at discharge, on a numeric rating scale (NRS) 0-10. Rescue opioids in oral morphine-equivalent doses (MME) were consecutively registered. Postoperative mobilization was registered twice daily.Overall mean pain were 2.0 (Cl 2.0-2.0) after THA and 2.3 (Cl 2.3-2.4) after TKA at rest, and 3.3 (Cl 3.3-3.3) and 3.7 (Cl 3.7-3.8) during mobilization, respectively. Patients undergoing TKA had a transient increase in pain intensity the day after surgery, whereas patients undergoing THA had improved pain levels. Outpatient criteria for pain (NRS < 5 during mobilization) were feasible for 37% of THA and 35% of TKA. Total median MME was 30.0 (0-573) after THA and 52.5 (0-390) after TKA. Patients undergoing TKA were less mobilized during hospitalization.A comparable number of THA and TKA cases were eligible for same-day discharge based on outpatient discharge criteria for pain. Patients receiving TKA can expect an increase in pain intensity and opioid needs on the day after surgery.