BACKGROUND: Low back pain affects a large proportion of the population. Transcutaneous electrical nerve stimulation (TENS) was introduced more than 30 years ago as an alternative therapy to pharmacologic treatments for chronic pain. However, despite its widespread use, the efficacy of TENS is still controversial. PURPOSE: The aim of this meta-analysis was to determine the efficacy of TENS in the treatment of chronic low back pain. METHODS: The authors searched MEDLINE, EMBASE, PEDro, and the Cochrane Controlled Trials Register up to June 1, 2000. Only randomized controlled clinical trials of TENS for the treatment of patients with a clinical diagnosis of chronic low back pain were included. Abstracts were excluded unless further data could be obtained from the authors. Two reviewers independently selected trials and extracted data using predetermined forms. DATA ANALYSIS: Heterogeneity was tested with Cochrane's Q test. A fixed effects model was used throughout for continuous variables, except where heterogeneity existed, in which case, a random effects model was used. Results are presented as weighted mean differences with 95% confidence intervals, where the difference between the treated and control groups was weighted by the inverse of the variance. Standardized mean differences were calculated by dividing the difference between the treated and control by the baseline variance. Standardized mean differences were used when different scales were integrated to measure the same concept. Dichotomous outcomes were analyzed with odds ratios. MAIN RESULTS: Five trials were included, with 170 subjects randomized to the placebo group receiving sham TENS and 251 subjects receiving active TENS (153 for conventional mode, 98 for acupuncture-like TENS). The schedule of treatments varied greatly between studies ranging from one treatment/day for 2 consecutive days, to three treatments/day for 4 weeks. There were no statistically significant differences between the active TENS group compared with the placebo TENS group for any outcome measures. Subgroup analysis performed on TENS application and methodologic quality did not demonstrate a significant statistical difference (P > 0.05). Remaining preplanned subgroup analysis was not conducted because of the small number of included trials and the variety of outcome measures reported. CONCLUSION: The results of the meta-analysis present no evidence to support the use or nonuse of TENS alone in the treatment of chronic low back pain. Considering the small number of studies responding to the criteria to be included in this meta-analysis, it is clear that more appropriately designed studies are needed before a final conclusion. Clinicians and researchers should consistently report the characteristics of the TENS device and the application techniques used. New trials on TENS should make use of standardized outcome measures. This meta-analysis lacked data on how TENS efficacy is affected by four important factors: type of applications, site of application, treatment duration of TENS, and optimal frequencies and intensities.