Background: Cochrane reviews aim to minimize bias by using explicit, systematic methods of high quality. Publication and selective outcome reporting bias are the Achilles heel of any systematic review. Registration at inception of trials in online clinical trial registries can reduce these biases by enabling reviewers to identify unpublished studies or outcomes. Objective: To explore the extent to which Cochrane reviewers search online clinical trial registries for ongoing and unpublished studies, how those search results are reported, and the possible impact thereof on the results of the review. Methods: We included all reviews of which the protocol was first published in the Cochrane Database of Systematic Reviews 2008. One reviewer (AvE) extracted data on whether trial registers and other sources of ongoing trials were searched, how this was reported, and how the identified ongoing or unpublished trials contributed to the authors conclusions. Results: To date we assessed only Issue 4, 2008 of the Cochrane Library and we included 40 reviews. (NB: at the Colloquium results regarding all 179 identified reviews will be presented). Searching for ongoing trials was performed in 31 of the 40 reviews (77.5%). Used methods were contacting experts (42.5%), handsearching of conference abstracts (50%), and online clinical trial registries (25%). Four reviews indentified extra studies through this additional search. Only one reviewer mentioned that not finding any unpublished studies could have led to bias. ClinicalTrials.gov was searched substantially more often (70%) than WHO ICTRP Search Portal (30%), by which 10 registries can be searched simultaneously. Conclusions: In this sample a majority of Cochrane reviews did not search online clinical trial registries for identifying ongoing and unpublished studies. In only a few reviews the possible impact of publication bias was explicitly mentioned. There’s a need for more guidance for identifying and addressing ongoing and unpublished trials.