In an attempt to understand the feasibility of future targeted genome optimization in agronomic crops, we tested the efficiency of homologous recombination-mediated sequence insertion upon induction of a targeted DNA double-strand break at the desired integration site in maize. By the development of an efficient tissue culture protocol, and with the use of an I-SceI gene optimized for expression in maize, large numbers of precisely engineered maize events were produced in which DNA integration occurred very accurately. In a subset of events examined in detail, no additional deletions and/or insertions of short filler DNA at the integration site were observed. In 30%–40% of the recovered events, no traces of random insertions were observed. This was true for DNA delivery by both Agrobacterium and particle bombardment. These data suggest that targeted double-strand break-induced homologous recombination is a superior method to generate specific desired changes in the maize genome, and suggest targeted genome optimization of agronomic crops to be feasible.