BACKGROUND: Little information exists to support that patients care about flexion beyond what is needed to perform activities of daily living (ADL) after Total knee arthroplasty (TKA). The purpose of this study was to investigate if the achievement of a higher degree of knee flexion after TKA would result in a better patient perceived outcome. METHODS: The study is a randomized, double-blinded, controlled trial in which 36 patients (mean age: 67.2 yrs) undergoing one-stage bilateral TKA randomly received a standard cruciate-retaining (CR) TKA in one knee and a high-flex posterior-stabilized (PS) TKA in the contra lateral knee. At follow-up ROM, satisfaction, pain, "feel" of the knee and the abilities in daily activities were assessed. RESULTS: At 1-year follow-up we found an expected significantly higher degree of knee flexion of 7[degree sign] in the high-flex knees (p = 0.001). The high-flex TKA's showed a mean active flexion of 121[degree sign]. In both TKA's the median VAS pain score was 0, the median VAS satisfaction score was 9, and the median VAS score of the patient "feel" of the knee was 9 at 1-year follow-up. Further, there were no significant differences between the knees in the performance of daily activities. CONCLUSIONS: As expected the high-flex TKA showed increased knee flexion, but no significant differences in the patient perceived outcomes were found. This suggests little relevance to the patients of the difference in knee flexion -- when flexion is of this magnitude -- as pain free ROM and high patient satisfaction were achieved with both TKA's.Trial registration: ClinicalTrials.gov: NCT00294528.