Objectives: Close to a tenth of all large truck crashes result from rolling over during some maneuver. The aim of this study was to identify causes of these serious events as well as preventive measures that could be taken to reduce their number. Methods: Detailed descriptions of 231 rollovers provided by field investigators were analyzed to identify causes. The descriptions addressed crash location, the nature of the crash, effect upon the vehicles involved, injuries and treatment, and contributing conditions. Causes were inferred from the nature of the crash. Results: Almost half of the rollover crashes resulted from failing to adjust speed to curves, loads, brake condition, road surfaces, and intersections. A second major contributor involved lack of attention, including general inattention, misdirected attention, falling asleep, and distraction. The third major factor involved control errors, including oversteering, understeering, overcorrecting for errors, and minor control errors. The remainder were not driving errors and included those of other drivers, those occurring before the truck took to the road, and the condition of the vehicle before it was driven. Conclusions: Although they account for but a tenth of all large truck crashes, rollovers result from causes that are relatively unique to the vehicle and where it is driven. Programs could improve safety through the use of video to expose truck drivers to the situations causing rollovers, along with simulation allowing drivers to experience the consequences of errors without the harmful results of actual rollovers.