Background. Previous systematic reviews have concluded that the effectiveness of motor control exercise for persistent low back pain has not been clearly established. Objective. The objective of this study was to systematically review randomized controlled trials evaluating the effectiveness of motor control exercises for persistent low back pain. Methods. Electronic databases were searched to June 2008. Pain, disability, and quality-of-life outcomes were extracted and converted to a common 0 to 100 scale. Where possible, trials were pooled using Revman 4.2. Results. Fourteen trials were included. Seven trials compared motor control exercise with minimal intervention or evaluated it as a supplement to another treatment. Four trials compared motor control exercise with manual therapy. Five trials compared motor control exercise with another form of exercise. One trial compared motor control exercise with lumbar fusion surgery. The pooling revealed that motor control exercise was better than minimal intervention in reducing pain at short-term follow-up (weighted mean difference=-14.3 points, 95% confidence interval [CI]=-20.4 to -8.1), at intermediate follow-up (weighted mean difference=-136 points, 95% CI=-22.4 to -4.1), and at long-term follow-up (weighted mean difference=-14.4 points, 95% CI=-23.1 to -5.7) and in reducing disability at long-term follow-up (weighted mean difference=-10.8 points, 95% CI=-18.7 to -2.8). Motor control exercise was better than manual therapy for pain (weighted mean difference=-5.7 points, 95% CI=-10.7 to -0.8), disability (weighted mean difference=-4.0 points, 95% CI=-7.6 to -0.4), and quality-of-life outcomes (weighted mean difference=-6.0 points, 95% CI=-11.2 to -0.8) at intermediate follow-up and better than other forms of exercise in reducing disability at short-term follow-up (weighted mean difference=-5.1 points, 95% CI=-8.7 to -1.4). Conclusions. Motor control exercise is superior to minimal intervention and confers benefit when added to another therapy for pain at all time points and for disability at long-term follow-up. Motor control exercise is not more effective than manual therapy or other forms of exercise.