A new and potentially devastating pest of oaks, Quercus spp., has been discovered in southern California. The goldspotted oak borer, Agrilus coxalis Waterhouse (Coleoptera: Buprestidae), colonizes the sapwood surface and phloem of the main stem and larger branches of at least three species of Quercus in San Diego Co., California. Larval feeding kills patches and strips of the phloem and cambium resulting in crown die back followed by mortality. In a survey of forest stand conditions at three sites in this area, 67% of the Quercus trees were found with external or internal evidence of A. coxalis attack. The literature and known distribution of A. coxalis are reviewed, and similarities in the behavior and impact of this species with other tree-killing Agrilus spp. are discussed.