Excision of the eroded lateral patellar facet has been suggested as an acceptable treatment for short-term pain reduction in patients with isolated patellofemoral osteoarthritis. The outcome of this procedure at long-term is however not known. We therefore reviewed the results of 155 consecutive patients (168 knees) treated at our institution with lateral facetectomy at an average follow up of 10.9years (±6.9years SD). During follow up 62 knees (36.9%) had failed and were revised to either TKA (60 knees), patellofemoral arthroplasty (one case) or total patellectomy (one case). Average time to reoperation in the failure group was 8.0years (±6.2years SD). Kaplan-Meier survival rates with reoperation as endpoint were 85% at 5years, 67.2% at 10years, and 46.7% at 20years respectively. At final follow up 79 (74.5%) of the knees that had not been re-operated were rated as either good or fair, which corresponds to 47% of the original group. Our study therefore demonstrates that a satisfactory outcome after lateral patellar facetectomy for isolated patellofemoral osteoarthritis can be expected in approximately half of the cases at 10year follow up.