DNA intercalation has found many diagnostic and therapeutic applications. Here, we propose the use of simple DNA intercalators, such as ethidium bromide, as tools to facilitate the error-free self-assembly of DNA nanostructures. We show that ethidium bromide can influence DNA self-assembly, decrease the formation of oligomeric side products, and cause libraries of multiple equilibrating structures to converge into a single product. Using a variety of 2D- and 3D-DNA systems, we demonstrate that intercalators present a powerful alternative for the adjustment of strand-end alignment, favor the formation of fully duplexed "closed" structures, and create an environment where the smallest, most stable structure is formed. A new 3D-DNA motif, the ninja star, was self-assembled in quantitative yield with this method. Moreover, ethidium bromide can be readily removed using isoamyl alcohol extractions combined with intercalator-specific spin columns, thereby yielding the desired ready-to-use DNA structure.