Unicondylar knee arthroplasty (UKA) has gained increasing popularity for treatment of unicompartmental arthritis, particularly in older less-demanding patients. Patient selection, implant design, and surgical technical features constitute the keys to successful results. The growing number of UKAs performed each year also highlights the possibilities and outcome of revision surgery. The two main causes of UKA revision are aseptic loosening and degradation of the contralateral side, which are associated to postoperative overcorrection of deformity in the frontal plane. Successful revision surgery can be achieved by total knee arthroplasty, but other possibilities exist to consider. Unicompartmental replacement has proven to be a reliable less invasive procedure than total knee arthroplasty, with lower morbidity, lower cost, earlier return to daily activities, and better joint kinematics. Thus, it is tempting to apply such advantages in cases that develop degenerative changes in the opposite compartment after a UKA with good initial results by implanting another UKA (BiUKA). This technique does not intend to repair a failed UKA, but only to resurface the secondly degenerated compartment responsible for a new set of complaints (different from those that motivated the first one). So absence of loosening and wear of the first prosthesis is mandatory, and patient selection criteria for UKA in the opposite compartment are required. Only moderate overcorrection after the first UKA (less than 5 degrees) assessed on pangonogram permits indication for BiUKA. Bone scan and arthroscopic evaluation are useful to confirm the state of the first implant and the biologic conditions of the other compartment. About the surgical approach, decision will be taken between preserving the initial one after adequate lengthening and creating a second. Recent studies have evaluated the outcomes of revision surgery after failed UKA, but there are only a few articles in literature regarding the BiUKA concept. The purpose of this report is to present our early experience including indications and selection criteria, surgical planning, step-by-step technique description, postoperative management, and early results (mean follow-up, 25.5 months; range, 12-42 months).