Study objective: To estimate the association between driver nationality and the risk of causing a collision between vehicles in motion. Design: Retrospective, matched by collision, case-control study. Setting: Collisions that occurred in Spain during the period from 1990 to 1999 were studied. Participants: Responsible (case) and non-responsible (control) drivers identified in the databases of the Dirección General de Tráfico (General Traffic Directorate) who were involved in a collisions between two or more four wheeled vehicles in motion, in which only one of the drivers had committed a traffic violation. Main results: Crude odds ratios (ORs) for the effect of driver nationality on the risk of causing a collision were significantly higher for foreign drivers than for Spanish drivers, and ranged from a minimum of 1.19 (95% CI 1.09 to 1.29) for Portuguese drivers to a maximum of 2.06 (1.88 to 2.27) for British drivers. Corresponding adjusted ORs were slightly lower, but were still significantly higher than 1 for all nationalities except Italian, Belgian, and American (USA). Adjusted ORs were usually higher for collisions that occurred in urban areas than on open roads. Conclusions: Authorities responsible for traffic safety, and drivers in general, should consider foreign drivers in Spain at particularly high risk for causing collisions, especially in urban areas.