BACKGROUND: Delayed union and non-union of fractures are a considerable cause of morbidity to patients. Laboratory studies have shown that electromagnetic fields can stimulate the formation of new bone, indicating a potential role for electromagnetic stimulation in the treatment of fractures that have failed to heal. OBJECTIVES: To assess the effects of electromagnetic stimulation for treating delayed union or non-union of long bone fractures in adults. SEARCH STRATEGY: We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (May 2010), the Cochrane Central Register of Controlled Trials (in The Cochrane Library 2010, Issue 2), MEDLINE (1966 to May 2010) and EMBASE (1980 to 2010 Week 20), trial registers and reference lists of articles. SELECTION CRITERIA: Randomised controlled trials evaluating electromagnetic field stimulation for the treatment of delayed union or non-union of long bones in adults. DATA COLLECTION AND ANALYSIS: Two authors independently selected studies and performed data extraction and risk of bias assessment. Treatment effects were assessed using risk ratios and, where appropriate, data were pooled using a random-effects model. MAIN RESULTS: Four studies, involving 125 participants, were included. Three studies evaluated the effects of pulsed electromagnetic fields and one study, capacitive coupled electric fields. Participants with delayed union and non-union of the long bones were included, but most data related to non-union of the tibia. Although all studies were blinded randomised placebo-controlled trials, each study had limitations.The primary measure of the clinical effectiveness of electromagnetic field stimulation was the proportion of participants whose fractures had united at a fixed time point. The overall pooled effect size was small and not statistically significant (risk ratio 1.96; 95% confidence interval 0.86 to 4.48; 4 trials). There was substantial clinical and statistical heterogeneity in this pooled analysis (I(2) = 58%). A sensitivity analysis conducted to determine the effect of multiple follow-up time-points on the heterogeneity amongst the studies showed that the effect size remained non-significant at 24 weeks (risk ratio 1.61; 95% confidence interval 0.74 to 3.54; 3 trials), with similar heterogeneity (I(2) = 57%).There was no reduction in pain found in two trials. No study reported functional outcome measures. One trial reported two minor complications resulting from treatment. AUTHORS' CONCLUSIONS: Though the available evidence suggests that electromagnetic field stimulation may offer some benefit in the treatment of delayed union and non-union of long bone fractures, it is inconclusive and insufficient to inform current practice. More definitive conclusions on treatment effect await further well-conducted randomised controlled trials.