This article examines the relative impact of socioeconomic status as a `fundamental cause\u27 of health disparities in Canada and the US. Fundamental cause theory suggests that persons of higher socioeconomic status have available a broad range of resources to benefit their health and therefore hold an advantage in warding off whatever particular threats to health exist at a given time. This leads to two predictions: (1) SES is more strongly associated with diseases that are more highly preventable than with less preventable diseases; and (2) SES has a stronger relationship to health in the US, where higher economic inequality and a lack of universal health insurance leads to a greater vying for resources. Findings indicate lower levels of SES increase the odds of experiencing a highly preventable disease relative to a less preventable disease in the US, but not in Canada, suggesting that social policies and level of economic inequality may buffer the relationship between socioeconomic resources and the incidence of preventable disease