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Trial registration was introduced to reduce research bias by promoting trial transparency and accountability. We aimed to evaluate the frequency of, and factors associated with, trial registration and declaration of trial registration.We selected all randomized controlled trials in kidney transplantation published between October 2005 and December 2010 and determined whether a trial was registered and whether a trial declared their registration in subsequent trial reports.Of 307 eligible trials identified, 24% (74/307) were registered, and of those, 59% (44/74) contained trial registration details within at least one trial report. Trial registration was more likely for trials published more than once, in later years or reported in journals that followed the International Committee of Medical Journal Editors guidelines. Trial registration was less likely for trials that did not declare their funding sources. Registered trials were more likely to declare registration details in related reports if published in later years or in a journal that followed International Committee of Medical Journal Editors guidelines. Trials that did not declare their funding sources were less likely to declare registration details.Although still suboptimal, the situation is improving over time, with both trial registration and declaration of registration details more likely in later years.