Recent US field data was used to evaluate the effectiveness of Electronic Stability Control (ESC) systems in reducing fatal crashes. Light vehicles with and without ESC systems were compared through comprehensive statistical analysis, including logistic regression and contingency analyses, to address ESC effectiveness in single- and multiple-vehicle, rollover and nonrollover crashes. Analyses controlled for key driver, vehicular, and environmental factors. Results indicate ESC systems are highly effective for rollovers in which the rollover is the first harmful event, but less effective for other rollovers and not effective for reducing fatal nonrollover crashes.