BACKGROUND:Treatments for managing articular cartilage defects of the knee, including drilling and abrasion arthroplasty, are not always effective. When they are, long-term benefits may not be maintained and osteoarthritis may develop, resulting in the need for a total knee replacement. An alternative is the surgical implantation of healthy cartilage cells into damaged areas (autologous cartilage implantation). OBJECTIVES:To determine the effectiveness of autologous cartilage implantation (ACI) in people with full thickness articular cartilage defects of the knee. SEARCH STRATEGY:We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (15 December 2005), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 3, 2005), MEDLINE (1966 to December 2005), CINAHL (1982 to December Week 2, 2004), EMBASE (1988 to 2005 Week 50), SPORTDiscus (1830 to January 2005) and the National Research Register Issue 3, 2005. SELECTION CRITERIA:Randomised and quasi-randomised trials comparing ACI with any other type of treatment (including no treatment or placebo) for symptomatic cartilage defects of the medial or lateral femoral condyle, femoral trochlea or patella. DATA COLLECTION AND ANALYSIS:Two review authors selected studies for inclusion independently. We assessed study quality based on adequacy of the randomisation process, adequacy of the allocation concealment process, potential for selection bias after allocation and level of masking. Data was not pooled due to clinical and methodological heterogeneity in the studies. MAIN RESULTS:We included four randomised controlled trials (266 participants). One trial of ACI versus mosaicplasty reported statistically significant results for ACI at one year, but only in a post-hoc subgroup analysis of participants with medial condylar defects; 88% had excellent or good results with ACI versus 69% with mosaicplasty. A second trial of ACI versus mosaicplasty found no statistically significant difference in clinical outcomes at two years. There was no statistically significant difference in outcomes at two years in a trial comparing ACI with microfracture. In addition, one trial of matrix-guided ACI versus microfracture did not contain enough long-term results to reach definitive conclusions. AUTHORS' CONCLUSIONS:The use of ACI and other chondral resurfacing techniques is becoming increasingly widespread. However, there is at present no evidence of significant difference between ACI and other interventions. Additional good quality randomised controlled trials with long-term functional outcomes are required.