OBJECTIVE: To determine clinical outcome and graft survivorship in patients undergoing autologous chondrocyte implantation (ACI) for the repair of chondral defects of the knee. DESIGN: Prospective cohort study. SETTING: 19 centers in the United States. PATIENTS: 50 patients (37 males, 13 females). Mean age was 36 years (range: 19-53). Defects were grade III or IV with a mean size of 4.2 cm 2. All patients had a minimum of 36 months postoperative follow-up. MAIN OUTCOME MEASUREMENTS: Clinician and patient evaluation based on the modified Cincinnati Knee Rating System. Graft failure was defined as replacement or removal of the graft due to mechanical symptoms or pain. RESULTS: Clinician and patient evaluation indicated median improvements of 4 and 5 points, respectively, at 36 months following ACI (p < 0.001). Previous treatment with marrow stimulation techniques and size of defect did not impact the results with ACI. The most common adverse events reported were adhesions and arthrofibrosis and hypertrophic changes. Three patients had graft failure and required reimplantation or treatment with alternative cartilage repair techniques. Kaplan-Meier estimated freedom from graft failure was 94% at 36 months postoperatively (95% CI = 88-100%). CONCLUSIONS: These results of this study indicate excellent graft survivorship using ACI as well as substantial improvement in functional outcome.