The determination of a motor vehicle's drag coefficient CD requires measurements of its aerodynamic resistance and its projected frontal area with high measuring accuracies. The presented paper gives an overview of optical methods for measuring projected areas, and describes a newly developed laser reflection system. It operates on a principle similar to that of a light-barrier system but in a reflection mode. With this optical device and a single numerically controlled traversing facility the outer enveloping contour of the vehicle is automatically tracked and the corresponding coordinates are recorded. The principle of the new measuring method, its advantages and results of measurements on test objects and vehicles are discussed in detail.