The method for examining trees comprises directing ground penetrating radar signals into a tree using a radar apparatus connected to a microprocessor control and data acquisition unit via an interface. The tree to be examined is scanned with the radar unit after the radar velocity for that tree is calibrated. The tree is scanned at a selected elevation either by moving a single radar unit along the bark of the tree in a circumferential manner or by moving a radar signal transmitter substantially diametrically opposed to a radar signal receiver along the bark of the tree in a circumferential manner. The microprocessor control and data acquisition unit controls the radar unit and stores and digitizes radar signals for generating a real-time radargram. A cross-sectional map of the tree, a map of the severity, shape, size and location of internal decay and a map of the thickness of remaining wood are then generated from the radargram and the ensemble of saved radar signals. The maps generated from this method may then be examined by tree diagnosticians to determine the extent of the internal damage of the tree.