PURPOSE OF THE STUDY Evaluation of short-term functional results in patients undergoing one-stage surgery involving sequential bilateral total knee arthroplasty (TKA) and comparison with the results of patients after unilateral TKA. MATERIAL AND METHODS The group with bilateral TKA consisted of 171 patients with 342 total knee replacements treated between 2009 and 2013. The control group included 50 patients with 50 TKAs operated on in the years 2010 to 2012. The indications to bilateral knee replacement included bilateral gonarthrosis, grade III or more in patients who were in good health and had a stable knee joint with axis deviation up to 20 degrees. A cemented TKA was used and the posterior cruciate ligament was preserved. Assessment of functional results was based on the Womac score, Knee Society Score (KSS 1, 2) range of motion and presence of specific complications in both groups. The follow-up lasted three years. RESULTS The average results in the bilateral vs the control group were as follows: the Womac score, 39.4/42.2 pre-operatively, 87.2/71.0 at 3 years; KSS 1, 48.5 / 44.8 pre-operatively, 87.4 / 79.9 at 3 years; KSS 2, 44.1 / 50.6 pre-operatively, 86.1 / 72.8 at 3 years; motion-flexion, 105.2° / 105.7° preoperatively, 114.0° / 100.2° at 3 years. In the bilateral group, infection was recorded in one patient. DISCUSSION Bilateral total knee replacement is a controversial issue. A higher risk of non-specific complications has been reported. Functional outcomes are good. The key problem is to set the correct indication to this procedure after an individual assessment of the patient's general health condition and the state of his/her knee joints. CONCLUSIONS The patients undergoing bilateral TKA at one-stage surgery showed functional results comparable (range of motion was even better) with the results of the unilateral TKA group. The number of specific complications was low. Every patient should be carefully assessed. Key words: total knee arthroplasty, bilateral implantation, functional results.