Engaging in online games has become increasingly important as a part of leisure activity in adolescents and adults. While the majority of people use these games in a healthy way, epidemiological studies show that some develop excessive use and symptoms that are related to those of substance-related addictions. Despite increasing research concerning the epidemiology of internet gaming disorder (IGD), predisposing factors have been examined to a lesser extent. Knowing about specific risk factors would help clarify the nosological features of IGD and enhance prevention and intervention. This study aimed to evaluate the relationships between personality traits and IGD. A total of 115 patients meeting the criteria for IGD were compared to 167 control subjects displaying either regular or intense use of online games. Additionally, 115 patients meeting diagnostic criteria for pathological gambling were included. IGD was associated with higher neuroticism, decreased conscientiousness and low extraversion. The comparisons to pathological gamblers indicate that low conscientiousness and low extraversion in particular are characteristic of IGD. An integration of personality variables into an etiopathological model describing presumable mechanisms fostering and maintaining addictive online gaming is proposed. This model could be helpful for the theoretical understanding of addictive gaming, public health campaigns and psychoeducation within therapeutic settings.