Fatigue is a risk factor involved in 10-25% of all road crashes. The aim of the present study is to examine factors influencing fatigue among HGV drivers in Norway and Greece, focusing especially on the role of national road safety culture. The study is based on survey data (N=201) and qualitative interviews (N=18) with HGV drivers in Norway and Greece. As previous studies indicate higher levels of aggression and conflicts in the Greek National RSC, we hypothesize that this will be related to higher levels of fatigue among the Greek drivers, as the National RSC is more exhausting. Results from logistic regression analyses support our hypothesis, indicating a relationship between National RSC and fatigue, controlled for the several key variables (e.g. work pressure, driving hours, type of transport). This conclusion is also supported by the results of the qualitative interviews, where Greek drivers report of an exhausting traffic environment, involving aggression and conflicts.