The Oxford-12 Item Knee Score is a recently developed and validated patient-completed outcome measure designed specifically for use with knee arthroplasty in the United Kingdom. We have translated this questionnaire into Swedish and tested the validity and reliability of the translated version in a cross-sectional study by a postal survey to 1,200 randomly selected patients from the Swedish Knee Arthroplasty Register. Swedish versions of the WOMAC, Nottingham Health Profile, SF-36, SF-12, and the Sickness Impact Profile were employed in the validation process. We also tested feasibility and patient-burden parameters. The translated version appeared to be linguistically and culturally equivalent to the original version with good validity and reliability. Indirect measures of responsiveness indicated that it is at least as responsive to relevant knee arthroplasty patient states as the previously validated Swedish version of the WOMAC. Application of the translated questionnaire to this population is feasible with minimal imposed patient-burden. The Swedish translation of the Oxford-12 Item Knee Score is a valid and reliable tool for outcome studies on knee arthroplasty patients.