The present Diploma Thesis aims at the investigation of the critical factors of motorcycle accidents in Greece, compared to passenger car accidents. For the achievement of this objective, appropriately processed data were used from the database of the Department of Transportation Planning and Engineering of the National Technical University of Athens (NTUA) and loglinear regression models were developed. The application of these models led to the investigation of the influence of several parameters, such as region type, age, lighting, accident type etc on the number of fatalities and injuries. It appears that the number of vehicles involved in the accident is the most important factor of the fatalities model, while the accident type affects more the serious and slight injuries. This influence is greater on motorcycles than passenger cars.