Although high rates of problem gambling have been identified among Internet gamblers, most studies have failed to identify the relative contribution of multiple forms of gambling as opposed to the exclusive participation in online forms. The aim of this study was to investigate differences in mental health status in exclusive online, exclusive land-based, and mixed Internet and land-based samples of gamblers drawn from the general population. A sample of 4594 respondents completing an online survey were categorised as exclusive online, land-based and mixed form gamblers. Participants completed a questionnaire eliciting demographic details, participation on all forms of gambling, use of alcohol, tobacco and drugs, help-seeking, and personal problems experienced due to gambling, as well as measures of problem gambling and psychological distress. Findings indicated that mixed gamblers exhibited higher problem gambling scores, level of gambling involvement, and consumption of alcohol during gambling than exclusive online gamblers. Land-based gamblers experienced higher levels of psychological distress, self-acknowledged need for treatment, and help-seeking behaviour. These findings suggest that exclusive online gamblers represent a different subpopulation at lower risk of harm compared to gamblers engaging in multiple forms. Understanding the characteristics of different problem gambling subpopulations may inform the development of more effective targeted interventions.