Unicompartmental knee arthroplasty (UKA) is a less invasive treatment for medial gonarthrosis. However, registry data have demonstrated higher revision and early failure rates. The purpose of this study is to report the early survivorship and failure modes in a series of 1000 consecutive medial mobile bearing UKA. UKA patients with a minimum of 2 year follow-up or those meeting the study endpoint (UKA failure or death) were included. Demographic variables, pre and post-operative clinical variables, and mode of failure were analyzed. Eight hundred and thirty-nine knees were included in the analysis. Forty revisions were performed at an average of 23.1 months (range, 2.3–74.2) following UKA for a survivorship of 95.2%. Indications for revision were aseptic loosening (15), tibial collapse (7), mobile bearing dislocation (2), persistent pain (12), progression of disease (2), infection (1), and tibiofemoral instability (1). These results are from a single center and may not be comparable to those of larger reports such as national registries.