PURPOSE: The aim of this study was to compare the long-term clinical and radiological results between fixed (FB) and mobile bearing (MB) implants with identical design from the same manufacturer. METHODS: From March 2007 to May 2009, we recruited 160 patients in a prospective, single centered, randomized controlled trial. The authors compared 81 FB total knee arthroplasty (TKA) versus 79MB with medial compartment osteoarthritis. The same posterior stabilized HLS Noetos knee prosthesis (CORIN) was used in all patients. The two groups only differed by the tibial insert (fixed or mobile). The authors compared the postoperative Knee Society Score (KSS), the passive clinical and active radiological knee flexion, the implant survivorship, the complications, and the presence of radiolucent lines. RESULTS: At mean 10.5years' follow-up (range 8-12.1years) no significant differences were found in clinical scores (KSS (p=0.54), pain score (p=0.77), stair climbing (p=0.44), passive maximum flexion (p=0.5)) or for radiological analyses (maximum active radiological flexion (p=0.06), presence of progressive radiolucent lines (5 (MB group) versus 6 (FB group); p=0.75)) between groups. No significant difference was found in overall implant survivorship (82% (MB group) versus 78% (FB group) p=0.58) or complication rate (p=0.32) at the last follow-up. CONCLUSION: No significant clinical and radiological differences were found between fixed and mobile bearing TKA using the same semi-constrained implant type with comparable overall survivorship. The choice between a fixed or mobile bearing implant should be based on surgeon preference and experience with the selected implant. LEVEL OF EVIDENCE: Prospective randomized controlled trial, Level II.