Of the 1000 consecutive unicompartmental knee arthroplasties (818 patients), 68% (678 knees) would be considered contraindicated based on published contraindications. At a mean follow-up of 10 years (5-17), there was no difference in American Knee Society (AKS) Objective Scores (P = .05) or Oxford Knee Score (P = .08) between groups. However, knees with contraindications had significantly (P = .02) fewer poor outcomes and significantly better AKS Functional Scores (P < .001) and Tegner Activity Scores (P < .001). At 15 years, no difference in implant survival (P = .33) was observed. The 3% of unicompartmental knee arthroplasties performed in young men (age <60) weighing 180 lb or over with high activity levels, who have been reported to have poor outcomes after fixed-bearing unicompartmental knee arthroplasty, had significantly better AKS Functional Scores (P < .001), Oxford Knee Score (P = .01), and Tegner Activity Score (P < .001) at 10 years. No difference in AKS Objective Scores (P = .54) at 10 years or implant survival at 15 years (P = .75) was seen.