The purpose of the current study was to compare midterm outcomes of posterior cruciate-retaining (CR) versus posterior cruciate-substituting (PS) procedures using the Genesis II total knee arthroplasty (TKA) system (Smith and Nephew, Memphis, TN). Ninety-nine (99) CR and 93 PS TKA's were analyzed in this prospective, randomized clinical trial. Surgeries were performed at seven medical centers by participating surgeons. Clinical outcomes (Knee Society Score, Range of Motion, WOMAC, SF-12, and Radiographic Findings), in addition to postoperative complications, were evaluated with a minimum follow-up of 5 years. Following data analysis, there were no significant differences in patient demographics or preoperative clinical measures between the two groups. At the latest follow-up interval, no significant differences were found between the CR and PS groups with regards to functional assessment, patient satisfaction, or postoperative complication. However, the PS group did display statistically significant improvements in range of motion when compared with the CR group. The results of this investigation would suggest that, while comparable in regards to supporting good clinical outcomes, the PS Genesis II design does appear to support significantly improved postoperative range of motion when compared with the CR design.