To evaluate the efficiency of ground-penetrating radar (GPR) to map root systems of urban trees in situ, this technique was tested on three trees in an urban environment. After carrying out the extremely rapid GPR tests around the bases of the sample trees, root systems were excavated with an air spade, which produces a supersonic jet of air used to remove soil from roots. Photographs were taken of root system transects for comparison with CPR images. Root system architecture was then quantified for one pine tree, and a two-dimensional image of the root system was reconstructed using AMAPmod software. A comparison of actual roots with images hand drawn from the GPR data showed that the technique is reliable for mapping large roots in the horizontal plane only. Most errors in data from the GPR method were induced when the root systems were manually redrawn, and from roots running parallel to the electromagnetic signal in the vertical plane. These roots could not be identified by GPR. The GPR technique could be considered a valuable nondestructive tool for the arborist, but it still needs development, especially with regard to a software that could reconstruct 3D images of root system architecture from raw data.