Our hypothesis was that a high-flexion rotating-platform posterior stabilized (RP-PS) design could maximize range of motion (ROM) and improve deep-flexion activities. Eighty-seven consecutive patients (109 knees) with high-flexion RP-PS design were prospectively followed up for a minimum of 3 years. Radiographic and clinical outcomes were analyzed using Knee Society Score criteria and Western Ontario and McMaster Universities Osteoarthritis Index. Good to excellent clinical scores were achieved in 96% of the knees. There were no cases of infection, malalignment, loosening, osteolysis, or spinout. The mean preoperative ROM improved from 110.7° to 124° postoperatively. High-flexion activities such as squatting and kneeling were achieved in 62% and 60% of patients, respectively. High-flexion knee implant is safe and improves ROM and deep-flexion activities. Persistent pain is an important cause of dissatisfaction after total knee arthroplasty.