The aim of this study was to evaluate the early results of a high flexion total knee prosthesis design and patient factors affecting the final range of motion (ROM) on a consecutive series of primary total knee arthroplasty (TKA) patients. 61 knees of 42 patients of a single surgeon series were prospectively evaluated. The mean follow up was 18 (13–30) months. The results were evaluated pre–and postoperatively using the Knee Society Score, the knee flexion and the difference between the preoperative and postoperative knee flexion angles (Δ flexion). Two tailed Student t test was used to compare preoperative and postoperative variables. Knee and function scores increased significantly from 33 (range 11–54) points and 41 (range 10–70) points to 94 (range 77–100) [p< 0,0001] and 89 (range 65–100) [p< 0,0001] respectively. ROM increased significantly [p< 0,0001] from 106 (range 20–140) to 124 (range 90–160) degrees. There was a strong correlation between the preoperative and postoperative flexion [r=0,5984 p=0,0002; (95% CI: r= 0,3210 to 0,7812)]. ROC (receiver-operating characteristic) curve analysis showed that to reach ≥ 130 degrees of final flexion using a high flexion knee system, the patient has to have minimum 100 degrees of flexion preoperatively. The use of high flexion knee system by itself should not be interpreted to bring flexion ≥ 130 degrees to every TKA patient, rather a design not to compromise ROM in selected patients.