Research suggests that Internet-based gambling includes risk factors that may increase gambling problems. The current study aimed to investigate subgroups of gamblers to identify the potential harms associated with various forms and modes of gambling. An online survey was completed by 4,594 respondents identified as Internet-only (IG), land-based only (LBGs), or mixed-mode (MMG) gamblers based on self-reported gambling behaviour in the last 12 months. Results showed significant socio-demographic differences between groups, with the LBGs being the oldest and MMGs the youngest. MMGs engaged in the greatest variety of gambling forms, had the highest average problem gambling severity scores, and were more likely to attribute problems to sports betting than the other groups. IGs were involved in the lowest number of divergent gambling activities, most likely to gamble frequently on sports and races, and attribute problems to these forms. Compared to the other groups, LBs had a higher proportion of problem gamblers than IGs and were most likely to play electronic gaming machines weekly, with this form of gambling contributing to problems at a substantially greater rate. This study confirms the importance of considering gambling involvement across subgroups of Internet or land-based gamblers. There is a need to consider the interaction between forms and modes of gambling to advance our understanding of the potential risk of mode of gambling to contribute to problems.