To examine the responsiveness of the EQ-5D-3L and EQ-5D-5L among total hip/knee replacement (THR/TKR) patients.|The EQ-5D (3L or 5L) and Western Ontario and McMaster University Osteoarthritis Index (WOMAC) have been routinely administered to all THR/TKR patients before and at 3 months after surgery in Alberta, Canada, since 2010. Patients were included in this analysis if they completed the WOMAC and the same version of EQ-5D at baseline and 3-month follow-up. The WOMAC was used as an anchor to categorize patients into 9 subgroups according to the relative change from baseline, i.e., no change, and 4 categories each for the amount of deterioration or improvement: large (≥ 70%), moderate (50% ≤ change < 70%), small but important (20% ≤ change < 50%), and very mild (0 < change ≤ 20%). The responsiveness of the EQ-5D-3L and EQ-5D-5L for each subgroup was assessed using effect size, standardized response mean, and Guyatt's Responsiveness Index.|A total of 1594 patients completed the EQ-5D-3L and WOMAC (60% females, mean age 66 years, N = 646 [41%] THR), and 3180 completed the EQ-5D-5L and WOMAC (60% females, mean age 66 years, N = 1352 [43.2%] THR) at baseline and 3-month follow-up. For both THR and TKR patients with "small but important" improvement, the EQ-5D-5L was consistently more responsive than the EQ-5D-3L.|Our study demonstrated that the EQ-5D-5L is more responsive than the EQ-5D-3L in identifying health-related quality of life changes in THR/TKR patients. We recommend using the EQ-5D-5L in longitudinal studies in this patient population.