The purpose of this paper is to examine the relationship between motor-carrier firm size and safety outcomes. Leveraging insights from the resource-based view of the firm, we develop hypotheses regarding this important relationship. To test our hypotheses, we constructed an original commercial motor-carrier safety database, drawing on data from the Motor Carrier Management Information System and the Safety Measurement System. The results demonstrate that there is a significant and positive relationship between firm size and safety performance as measured through a carrier’s number of crashes, unsafe driving violations, hours-of-service compliance, and vehicle maintenance violations. The impact of firm size on safety performance varies according to industry segment. This study has important academic and public policy implications.