Background and Purpose. Weakness in partially paralysed muscles is a disabling impairment for people with neurological conditions. Strength training programmes are widely administered to address this impairment. There is a common belief that the effectiveness of strength training programmes can be enhanced by the addition of electrical stimulation. The purpose of this systematic review was to assess the efficacy of electrical stimulation for increasing voluntary strength in people with neurological conditions. Method. Eligible randomized trials of electrical stimulation were identified by searches of computerized databases. The search yielded 11 267 abstracts, of which 60 were retrieved. Two assessors independently reviewed full text versions of these articles. Results. Eighteen studies satisfied the inclusion criteria. These studies involved participants with spina bifida (n = 1), cerebral palsy (n = 1), peripheral nerve lesion (n = 1), multiple sclerosis (n = 1), spinal cord injury (n = 3) and stroke (n = 11). The mean (SD) PEDro score for trial quality was 4.9 (1.0) out of 10. Meta-analyses of studies involving similar patients were not done because of insufficient data or lack of homogeneity. The results of all studies were analysed individually. Conclusion. Several studies suggest a modest beneficial effect of electrical stimulation in patients with stroke. It is not clear whether patients with other types of neurological disabilities benefit from electrical stimulation in the same way. Copyright © 2007 John Wiley & Sons, Ltd.