Background: As exposure to tobacco smoke pollution (TSP) has been identified as a cause of premature death and disease in non-smokers, and studies have demonstrated that smoking in cars produces high levels of TSP, this study will investigate smokers' rules for smoking in their cars, and predictors of car smoking rules, including potentially modifiable correlates. Methods: Data were drawn from nationally representative samples of current smokers from the International Tobacco Control Policy Evaluation Project surveys in France (2007), Germany (2007), and the Netherlands (2008). Smokers in France and Germany were asked about smoking rules in their cars, and smokers in the Netherlands were asked about smoking rules in cars carrying children. Results: In France and Germany, 59% and 52% of smokers respectively, allowed smoking in their cars. In the Netherlands, 36% of smokers allowed smoking in cars carrying children. Predictors of allowing smoking in cars included: being a daily vs. non-daily smoker, being younger vs. older age, having no (young) children in the home, being a heavier smoker, and allowing smoking in the home. In the Netherlands, smokers who agreed that TSP is dangerous to non-smokers were less likely to allow smoking in cars carrying children. Conclusion: Overall, a sizeable proportion of smokers allowed smoking in their cars across the three countries. Media campaigns with information about the dangers of TSP may increase the adoption of smoke-free cars. These media campaigns could target smokers who are most likely to allow smoking in cars.