BACKGROUND: Acupuncture is widely used for the treatment of headache, but its effectiveness is controversial. OBJECTIVES: To determine whether acupuncture is: - more effective than no treatment - more effective than 'sham' (placebo) acupuncture - as effective as other interventions used to treat idiopathic (primary) headaches. SEARCH STRATEGY: Electronic searches were performed in MEDLINE, EMBASE, the Cochrane Controlled Trials Register, and the database of the Cochrane Field for Complementary Medicine. We also contacted researchers in the field and checked the bibliographies of all articles obtained. SELECTION CRITERIA: Randomized or quasi-randomized clinical trials comparing acupuncture with any type of control intervention for the treatment of idiopathic (primary) headaches were included. DATA COLLECTION AND ANALYSIS: Information on patients, interventions, methods, and results was extracted by at least two independent reviewers using a pre-tested standard form. Results on headache frequency and intensity were summarized descriptively. Responder rate ratios (responder rate in treatment group/responder rate in control group) were calculated as a crude indicator of results for sham-acupuncture-controlled trials. Quantitative meta-analysis was not possible due to trial heterogeneity and insufficient reporting. MAIN RESULTS: Twenty-six trials including a total of 1151 patients (median, 37; range, 10-150) met the inclusion criteria. Sixteen trials were conducted among patients with migraine, six among patients with tension-type headache, and four among patients with various types of headaches. The majority of trials had methodological and/or reporting shortcomings. In eight of the 16 trials comparing true and sham (placebo) acupuncture in migraine and tension-type headache patients, true acupuncture was reported to be significantly superior; in four trials there was a trend in favor of true acupuncture; and in two trials there was no difference between the two interventions. (Two trials were uninterpretable.) The 10 trials comparing acupuncture with other forms of treatment yielded contradictory results. REVIEWER'S CONCLUSIONS: Overall, the existing evidence supports the value of acupuncture for the treatment of idiopathic headaches. However, the quality and amount of evidence are not fully convincing. There is an urgent need for well-planned, large-scale studies to assess the effectiveness and cost-effectiveness of acupuncture under real-life conditions.