Online gambling and gaming are associated with Problematic Usage of the Internet (PUI) in subgroups of individuals. This study aimed to assess how different personality dimensions are associated with PUI scores of Massively Multiplayer Online Role Playing Games (MMORPG) players and online poker players, and to characterize common and specific personality traits of both groups in their association with PUI. Participants (N = 1144) were recruited online and assessed with the Internet Addiction Test (IAT), the Big Five Inventory and the Short UPPS-P Impulsive Behavior Scale. Data were analyzed with multiple robust linear regression models. The first model tested the associations between personality and impulsivity traits with IAT scores, while controlling for age, gender, and type of online activity. The second model included interaction terms to assess whether these associations differed between MMORPG and poker players. In model 1, neuroticism, negative urgency, positive urgency and sensation seeking were significantly and positively associated with higher IAT scores after controlling for the other personality traits, age, gender, and type of online activity. Extraversion was negatively associated with IAT scores. In Model 2, no significant difference in how these personality traits relate to IAT scores was observed between the two groups. Results highlight that traits such as neuroticism, negative urgency, positive urgency, and sensation seeking constitute potential risk factors for PUI, while extraversion might constitute a protective factor against PUI. The identified associations could be useful in understanding players’ attitudes and supporting them in gaining insight into their difficulties.