It is debatable whether high flexion total knee arthroplasty (TKA) designs will improve postoperative flexion, function or will diminish the need for manipulation under anesthesia (MUA). We retrospectively analyzed range of motion (ROM), flexion, Knee Society Score (KSS), and rate of MUA in a consecutive group of patients who underwent TKA with a conventional PS or a high flexion (HF) insert using identical surgical technique, implant design and postoperative care. Fifty TKAs with a standard posterior stabilized insert (PS) were matched with 50 who received a high flexion insert (HF) for patient’s age, gender, preoperative ROM, and KSS. The patient’s ROM and KSS were obtained at 6 weeks, 4 months, and 1 year postoperatively. The outcome variables (flexion, ROM, KSS and manipulation rate) in the two groups were compared using the generalized estimating equations method. A second analysis of patients with preoperative flexion equal or greater than 120 degrees was performed. The ROM, flexion, and patient reported KSS was similar in the PS and HF groups at each one of the time periods. The rate of MUA was also similar. Patients with a preoperative ROM of at least 120° showed similar results. Our study found that 1 year after surgery, patients who underwent TKA with a PS or a HF insert achieved similar flexion, ROM and function.