The fad of do-it-yourself automobile customizing began in the late 1930s with cropped roofs. Today, this practice of altering the vehicle from the “as-built” condition continues, offsetting in most cases, the manufacturers' safety design improvements. The purpose of this paper is to call attention to some of these alterations that have compromised occupant safety, using examples from actual field accidents.Some of the situations illustrated show that tachometers and other miscellaneous devices which are attached to the steering column abort the compressibility of the energy-absorbing device, increasing chest injuries. These add-ons are also injury sites for the upper and lower limbs.Another modification is to alter the suspension geometry to achieve a dragster appearance. The raising of the rear end exposes the fuel tank, normally protected by the rear structure from direct contact by another vehicle in a rear-end collision situation. An example of how these changes increase the injury risk to an occupant of the striking car is shown.Other items include upper and lower instrument panel alterations and add-ons, visibility, removal of headrests, and maintenance. The magnitude of the role played by these owner modifications is not known, but case studies confirm that they are factors in the annually reported traffic deaths and injuries.