31 randomized or quasi-randomized controlled trials (n=1690) evaluating the effects of exercise on pain and function in patellofemoral pain syndrome were included in this study. The purpose of this systematic review and meta-analysis was to qualitatively and quantitatively (19 studies included in quantitative assessment) assess the available literature regarding the efficacy of exercise therapy in adolescents and adults with patellofemoral pain syndrome. The quality of evidence available was 'very low' based on assessment using the GRADE working group criteria, but suggested that exercise therapy significantly improved pain and functional ability in the short and long term (under or over 3 month follow-up) when compared to control groups.