The objective of this research is the analysis of the effect of lorries and buses on the number of road accidents and related casualties in Greece. For this purpose, the NTUA database with disaggregate road accident data was exploited. In particular, a comparative analysis of all road accidents and related casualties with or without the involvement of lorries and buses was carried out, for different road network types, vehicle types, accident types and driver characteristics. Specific analysis techniques were implemented in order to deal with the lack of related exposure data (e.g. vehicle kilometres of travel), such as the calculation of accident severity rates and fatality distributions per accident type. The results revealed important involvement of lorries and buses in road accidents in Greece, rising up to more than 16% of all road accidents and more than 20% of all fatalities. As regards road accident severity, it was found that the number of fatalities per accidents in accidents with lorry or bus involvement is almost double than the related severity rate in accidents without lorry or bus involvement. However, the respective difference in accident severity for injured persons was not statistically significant. Moreover, lorries and buses are clearly over-represented in head-on or at-angle collisions. The results of this analysis may be useful for the planning and implementation of specific measures for the traffic management of lorries and buses, in order to decrease road accident involvement and severity of lorries in Greece, both in urban and interurban roads.