In this article, we examine the relationship between safety culture and national culture, and the implications of this relationship for international safety culture assessments. Focussing on Hofstede's uncertainty avoidance (UA) index, a survey study of 13,616 Air Traffic Management employees in 21 European countries found a negative association between safety culture and national norm data for UA. This is theorized to reflect the influence of national tendencies for UA upon attitudes and practices for managing safety (e.g., anxiety on risk; reliance on protocols; concerns over reporting incidents; openness to different perspectives). The relationship between UA and safety culture is likely to have implications for international safety culture assessments. Specifically, benchmarking exercises will consistently indicate safety management within organizations in high UA countries to be poorer than low UA countries due to the influence of national culture upon safety practices, which may limit opportunities for identifying and sharing best practice. We propose the use of safety culture against international group norms (SIGN) scores to statistically adjust for the influence of UA upon safety culture data, and to support the identification of safety practices effective and particular to low or high UA cultures.