We performed, with strict criteria, bilateral simultenaous medial compartment knee arthroplasty (under the same anesthesia) with a mobile insert (artificial meniscus) in our Iatriko Psychikou Clinic in Athens on a 60-year-old patient with a very good general condition and a good muscular system. Simultaneous alignment of the patella on both sides with cartilage lesions due to chondropathy and overpressure of the external compartment with release of the external retinaculum. Immediately up and with full weight bearing, no need for blood transfusion, 48 hour hospital stay, walking without any assistance, full range of motion, totally happy patient. But, we do not recommend simultaneous knee arthroplasty on both knees on the same day in patients with vascular, cardiac and other important general problems. For us it is an easy procedure but for some elderly patients, especially the risk of complications increases based on the international references. In these cases, it is better to perform knee arthroplasty on a separate day for each knee. Patients must be selected carefully!