The emerald ash borer, Agrilus planipennis Fairmaire, is a serious exotic pest of ash trees in North America. One of the greatest challenges facing its successful management is the ability to accurately detect it in a tree. The within-tree distributions of A. planipennis feeding galleries were described in relation to height-above-ground, stem diameter, bark thickness and stem aspect. Gallery distributions were bounded by a minimum stem diameter of approximately 5 cm, a minimum bark thickness of approximately 2 mm and a maximum height above ground of 7 m. Galleries were found most often on the southwest side of the tree. A maximum bark thickness of approximately 4.5 mm was observed in trees that had been attacked for only one year, but not in trees that had more than one year of attack. To increase the probability of detecting new A. planipennis infestations, initial searches should be made in trunk sections and branches with diameters of approximately 7 cm.