Patellofemoral pain syndrome (PFPS) is one of the most commonly reported injuries in sports medicine. 10,11,38 PFPS is characterized by diffuse retropatellar and peripatellar pain that is aggravated with squatting, prolonged sitting, and stair activities, and is diagnosed in the absence of other pathologies, such as patellar tendinopathy, chondral defects, or patellofemoral osteoarthritis. 12,25,39 Although quadriceps muscle-strengthening exercises are often included as part of the intervention for PFPS, 7,16 the most recent literature review, published in 2003 by Heintjes et al, 16 concluded that there was little evidence to support exercises as an intervention. However, this conclusion was based on the results of only 2 randomized controlled trials (RCTs) and 1 clinically controlled trial. 16Since the review by Heintjes et al, 16 a number of studies investigating the effectiveness of quadriceps strengthening for the treatment of PFPS have been published. Therefore, an updated thorough review of the literature on the clinical effectiveness of quadriceps-strengthening exercises appears warranted. The aim of this systematic review was to evaluate and summarize the evidence for therapist-guided quadriceps muscle-strengthening exercises (alone or combined with other interventions) as a treatment for PFPS when compared to advice and information or a placebo treatment. T T OBJECTIVE:To summarize the evidence for physical therapist-guided quadriceps-strengthening exercises as a treatment for patellofemoral pain syndrome. T T BACKGROUND:Although quadriceps strengthening is often included in the plan of care for patellofemoral pain syndrome, a systematic review published in 2003 found only limited evidence that exercise was more effective than no exercise for this common condition. T T METHODS:The PubMed, Embase/MEDLINE, and Cochrane Central Register of Controlled Trials databases, from inception to January 9, 2014, were searched for randomized controlled trials comparing the use of quadriceps-strengthening exercises to interventions consisting of advice/information or a placebo. Outcomes of interest were pain measures and function, as measured with selfreport questionnaires. The methodological quality of the randomized controlled trials was assessed with the Physiotherapy Evidence Database scale. Results were summarized using a best-evidence synthesis and graphically illustrated using forest plots without meta-analysis. T T RESULTS:Seven studies were included in the literature review. These studies reported strong evidence that isolated quadriceps strengthening is more effective in reducing pain and improving function than advice and information alone. In addition, compared to advice and information or placebo, there was strong evidence that quadriceps-strengthening exercises combined with other interventions may be more effective in reducing pain immediately postintervention and after 12 months, but not in improving function. T T CONCLUSION:The literature provides strong evidence for the use of quadriceps-strengtheni...