Background: Systematic reviews play a decisive role in the transfer of knowledge into medical practise. Clinical trials can be seen as the backbone of systematic reviews. To our knowledge, this study is the first to examine the production of clinical trials in the field of complementary and alternative medicine (CAM) and the second to investigate the country of origin for trials across all specialties. Objectives: To determine the country of origin of clinical trials used in Cochrane reviews (CRs). Methods: A random sample was drawn from a database of publications used for CRs published in Issue 1, 2008 of the Cochrane Database of Systematic Reviews. In addition, we selected a random sample of publications used in CRs in the field of CAM. Abstracts and/or full texts were checked to determine the likely country of origin. This decision was based on participating centres, responsible ethics committees, funding sources, and affiliation of the authors. Results: We randomly selected 1,000 out of 140,005 references across all specialities. After de-duplication, 959 studies were assessed in further detail, of which in 876 (91%) the country of origin was determined (Table 1). Furthermore, 500 studies in the field of CAM were randomly selected. The likely country of origin was determined in 449 (92%) of 490 assessed studies (Table 1). Conclusions: The results suggest that the USA and the UK lead the way in publishing the greatest number of scientific trial reports. However, China is also a major contributor to research in the field of CAM. Taking into account sizes of population and economic power, countries like France, Germany, Italy and Spain make relatively small contributions. In contrast, smaller countries like Australia, Denmark, Finland, New Zealand and Sweden play a major role.