Until recent years there has been no evidence from randomized controlled trials (RCTs) on the efficacy of deep brain stimulation (DBS) for Parkinson's disease (PD). This review and meta-analysis of RCTs describes the efficacy of DBS in improving motor signs, functionality and quality of life of PD patients. Several electronic databases were consulted up to April 2013. RCTs that compared DBS plus medication versus medication (alone or plus sham DBS) in PD patients were included. Outcome measures were motor function, waking time on good functioning without troublesome dyskinesias, levodopa-equivalent dose reduction, medication-induced complications, activities of daily living, health-related quality of life, and neurocognitive and psychiatric effects. Six RCTs (n = 1,184) that compared DBS plus medication versus medication alone were included. The results show that DBS significantly improves patients' symptoms, functionality and quality of life. Effects sizes are intense for the reduction of motor signs and improvement of functionality in the off-medication phase, in addition to the reduction of the required medication dose and its associated complications. Moderate effects were observed in the case of motor signs and time in good functionality in the on-medication phase, in addition to the quality of life. Although the number of RCTs obtained is small, the total sample size is relatively large, confirming the efficacy of DBS in the control of motor signs and improvement of patients' functionality and quality of life. More controlled research is required on the neurocognitive and psychiatric effects of DBS.