Introduction: This study evaluated the effect of both postoperative residual varus alignment and the amount of correction in lower limb alignment (LLA) on postoperative functional outcomes of total knee arthroplasty TKAs in patients with preoperative varus deformity. Methods: Two-hundred and fifty-two knees of 209 patients who underwent a TKA for treating varus gonarthrosis were retrospectively reviewed in the study. Patients were then divided into the three groups according to the postoperative hip-knee-ankle angle (HKAA): the neutral group (NG) (HKAA: 183°-177°); the mild varus group (HKAA: 176.9°-174°); and the severe varus group (HKAA <174°). Patients were also categorized into the three groups based on the amount of correction in LLA; group A (<5); group B (5° to 10°), and group C (>10°). Pre- and post-operative functional outcomes were compared among the groups. Results: There were no significant differences in the postoperative Knee Society Score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and visual analog scale (VAS) scores between the mild and NGs (p=0.99, p=0.62, and p=0.33, respectively). The severe group showed lower postoperative KSS, WOMAC, and higher VAS scores compared to other two groups (p<0.001, p<0.001, and p<0.001, respectively). No significant differences were observed in the postoperative knee flexion and extension deficits among the three groups (p=0.79 and p=0.3). Patients with correction in LLA of >10° had higher WOMAC and lower VAS scores than the other patients (p=0.008 and p=0.002, respectively). Conclusion: Postoperative mild varus deformity is not associated with poorer clinical and functional outcomes; however, a postoperative severe varus deformity following TKA can cause a significant deterioration in postoperative clinical and functional outcomes in patients with preoperative varus osteoarthritis.