Purpose: We systematically reviewed the evidence on the efficacy and safety of sacral nerve stimulation (SNS) for severe urge incontinence. Materials and Methods: A systematic review was performed of primary studies of SNS for urge incontinence published in English between 1966 and May 2003, and identified in major electronic databases. Two reviewers independently selected studies, assessed their methodological quality and extracted data. Results: Four randomized controlled trials and 30 case series were identified. Evidence from the randomized controlled trials, involving approximately 120 patients, showed that; about 80% achieved continence or greater than 50% improvement in their main incontinence symptoms after SNS compared with about 3% of controls receiving conservative treatments while waiting for an implant. While case series were larger, they were methodologically less reliable. However, they showed similar results with 67% of patients becoming dry or achieving a greater than 50% improvement in symptoms after implantation. Incontinence episodes, leakage severity, voiding frequency and pad use were significantly lower after implantation. Benefits were reported to persist 3 to 5 years after implantation. Adverse events were documented in 27 studies. Overall the reoperation rate in implanted cases was 33%. The most common reason for surgical revision was relocation of the generator because of pain and infection. Common complications were pain at the implant or lead site in 25% of patients, lead related problems such as lead migration in 16%, replacement and repositioning of the implanted pulse generator in 15%, wound problems in 7%, adverse effects on bowel function in 6%, infection in 5% and generator problems in 5%. Permanent removal of the electrodes was reported in 9% of patients. Technical changes with time have been associated with decreased complication rates. Conclusions: There is evidence indicating that SNS is effective for decreasing symptoms in patients with urge incontinence. Adverse events occurred in about half of the implanted cases and surgical revision was performed in 33%. No major irreversible complications were reported in the studies reviewed. Further research is required on the long-term effects of and quality of life in patients with SNS.