The Medline, Pubmed, Embase, Cinahl and PEDro databases and the Cochrane controlled trials register were searched for RCTs of subjects with knee osteoarthritis comparing aerobic walking or home-based quadriceps strengthening exercise with a non-exercise control group. The methodological quality of retrieved RCTs was assessed. Outcome data were abstracted for pain and self-reported disability, and the effect size calculated for each outcome. RCTs were grouped according to exercise mode and the data pooled using both fixed and random effects models. Thirty-five RCTs were identified, 13 of which met inclusion criteria and provided data suitable for further analysis. Pooled effect sizes for pain were 0.52 for aerobic walking and 0.39 for quadriceps strengthening. For self-reported disability, pooled effect sizes were 0.46 for aerobic walking and 0.32 for quadriceps strengthening.