OBJECTIVES: To examine health-related quality of life (HRQoL) following total knee replacement (TKR) or unicompartmental knee arthroplasty (UKA). METHODS: Asian adult patients undergoing either TKR or UKA in a hospital of Singapore between 2001 and 2006 were interviewed before surgery and 6 and 24 months postoperatively to obtain demographic information and HRQoL scores using the Short-Form (SF-36) and the Oxford Knee Score (OKS). RESULTS: Data were collected from 2243, 1715, and 1113 patients at baseline, 6, and 24 months, respectively. TKR patients had a lower preoperative score than UKA patients on OKS and four subscales of the SF-36 (p <0.01). Both TKR and UKA patients’ OKS and SF-36 subscale scores improved six months postoperatively except in the general health domain. SF-36 role physical (RP) and bodily pain (BP) scores showed the most improvement (40.9 and 33.0 points in TKR and 36.9 and 31.4 points in UKA patients, respectively). The most substantial improvements between baseline and two years after surgery were in the physical domains of HRQoL (RP, BP, and physical functioning (PF)). In addition, in both groups, five domains of SF-36 (RP, BP, PF, social functioning, and role limitations due to emotional problems) reached the proposed minimal clinically important difference of ten points. TKR patients’ SF-36 and OKS scores were not significantly different from those of UKA patients two year after surgery, except PF scores. Multiple regression analysis adjusting for sociodemographics showed that baseline scores were a significant predictor of the postoperative scores of OKS and all SF-36 subscales (p <0.01), whereas the type of surgery was not associated with the postoperative scores. CONCLUSIONS: Both TKR and UKA patients experienced significant improvements in HRQoL, particularly in the RP and BP domains. After controlling for potential confounding variables, the type of surgery was not a significant predictor of patients’ postoperative HRQoL scores.