There is increasing controversy about the appropriate role of the local institutional review board in the review of multicenter clinical studies. We evaluated the effects of the local review process at 25 study sites on the consent forms from two studies of the Tuberculosis Trials Consortium, a multicenter trials group. Two independent reviewers classified all changes made in the centrally approved consent forms; a third reviewer evaluated those changes if the two initial reviewers disagreed. The median time to initial local approval was 104.5 days (range 31-346). There were no changes in the study protocols as a result of local review. Consent forms became longer and less readable after local review, with a mean increase in grade level of 0.9 (+/-0.9) reading grade levels (p<0.001). A median of 46.5 changes (range 3-160) were made in the centrally approved forms. Most changes (85.2%) involved altering wording without affecting meaning. Errors were commonly introduced (11.2% of changes), and 33 of 50 (66%) locally approved consent forms contained at least one error in protocol presentation or a required consent form element. Local approval of two multicenter clinical trials was time-consuming and resulted in many changes in centrally approved consent forms. These changes frequently decreased readability and introduced errors.