With their extensive data and specimen repositories, clinical trials are a long-term, valuable resource to health researchers. However, assuring protection of participants' rights can be challenging, particularly when such trials are conducted at multiple sites with multiple Institutional Review Boards (IRBs). One little-used mechanism that can streamline IRB review in multisite trials while maintaining participants' protections is the single-study IRB Cooperative Agreement. This agreement is entirely different from reciprocity agreements between institutions. Beginning in 1996, the Beta-Carotene and Retinol Efficacy Trial established single-study IRB Cooperative Agreements among its performance sites, which reduced the average time to complete IRB approval from over 6 months to 1 month for each of many substudies. We describe our experience and make recommendations for other multisite clinical trials.