To compare the efficacy of aerobic walking and home based quadriceps strengthening exercises in reducing pain and disability in knee osteoarthritis. Systematic review of randomised controlled trials. People with knee osteoarthritis. Comparison of aerobic walking or home based quadriceps strengthening exercise with a non-exercise control group. Strengthening exercise was considered to be ‘home based’ where it was undertaken exclusively in the subject's home environment or, where exercise was partly supervised, the regimen was intended to be continued at home unsupervised. Pain and disability. 13 studies were included. One study provided a direct comparison between aerobic walking and home based strengthening exercises and control. Nine RCTs evaluated quadriceps strengthening exercises, and in three studies the exercise intervention was predominantly aerobic walking. Control interventions included education and lifestyle advice, support by telephone calls, and no intervention. When comparing aerobic walking with no exercise interventions, the pooled effect sizes for pain and disability were 0.52 (95% CI 0.34 to 0.70) and 0.46 (95% CI 0.25 to 0.67) respectively. Corresponding effect size for quadriceps strengthening was 0.32 (95% CI 0.23 to 0.42) for both pain and disability. Both aerobic walking and home based quadriceps strengthening exercises are effective at reducing pain and disability in subjects with knee osteoarthritis. No advantage of one form of exercise over the other was found on indirect comparison.