Objectives: This research aims to identify and analyze the factors affecting accident severity through a macroscopic analysis, with focus on the comparison between inside and outside urban areas. Disaggregate road accident data for year 2008 in Greece were used.Methods: Two models were developed, one for inside and one for outside urban areas. Since the dependent variable had two categories, Killed/Severely Injured (KSI) and Slightly Injured (SI), the binary logistic regression analysis was selected. Furthermore, this research aims to estimate the probability of fatality/severe injury versus slight injury as well as to calculate the odds ratios (relative probabilities) for various road accident configurations. The Hosmer and Lemeshow statistic and other diagnostic tests were conducted in order to assess the goodness-of-fit of the model.Results: From the application of the models, it appears that inside urban areas three types of collision (sideswipe, rear-end, with fixed object/parked car), as well as involvement of motorcycles, bicycles, buses, two person’s age groups (18–30 and older than 60 years old), time of the accident and location of the accident seem to affect accident severity. Outside urban areas, four types of collision (head-on, rear-end, side, sideswipe), weather conditions, time of the accident, one person’s age group (older than 60 years old) and involvement of motorcycles and buses were found to be significant.Conclusions: Factors affecting road accident severity only inside urban areas are young drivers, bicycles, intersections and collision with fixed objects, whereas factors affecting severity only outside urban areas are weather conditions, head-on and side collisions, demonstrating the particular road users and traffic situations which should be focused for road safety interventions for the two different types of network (inside and outside urban areas). The methodology and the results of this research may be proved a promising tool to prioritize programs and measures to improve road safety in Greece and worldwide.