Background. No study compared the clinical results of the posterior-stabilized mobile-bearing knee with those of nonposterior-stabilized mobile-bearing knee in the same patients. The purpose of this study was to examine whether the clinical and radiographic results, range of motion, patients satisfaction, and complication rates would be better in the knees with a posterior-stabilized mobile-bearing knee than in the knees with a nonposterior-stabilized mobile-bearing knee. Methods. One hundred and fourteen patients (mean age, 67.9 years) received a nonposterior-stabilized mobile-bearing knee prosthesis in one knee and a posterior-stabilized mobile-bearing knee prosthesis in the contralateral knee. Seven patients were men, and 107 were women. At the time of each follow-up (mean, 7.3 years; range, seven to 7.6 years), the patients were assessed clinically and radiographically. Results. The mean postoperative Knee Society knee score (95 points versus 96 points, p=0.176), Hospital for Special Surgery knee score (92 points versus 93 points, p=0.077), and Western Ontario and McMaster University Osteoarthritis score (21 versus 20 points, p=0.785) were similar between the two group. At the final follow-up, the average range of motion was 27.7° (range, 70° to 150°) in the knees with a nonposterior stabilized mobile-bearing prosthesis and it was 132° (range, 90 to 150 °) in the knees with a posterior-stabilized mobile-bearing prosthesis. Complication rates (2.6% versus 1.8%) were similar between the two groups. The estimated survival rate was 97.4% at eight years with an overall revision rate of 2.6% (three of 114 knees) in the nonposterior-stabilized mobile-bearing prosthesis group and 98.2% at eight years with an overall revision rate of 1.8% (two of 114 knees) in the posterior-stabilized mobile-bearing prosthesis group. Conclusions. After a minimum duration of follow-up of seven years, we found no significant differences between the two groups with regard to the clinical and radiographic results, or patient satisfaction, or complication rate. However, the posterior-stabilized mobile-bearing prosthesis group had a greater range of knee motion than the nonposterior-stabilized mobile-bearing prosthesis group