Numerous studies have reported higher rates of gambling problems among Internet compared with non-Internet gamblers. However, little research has examined those at risk of developing gambling problems or overall gambling involvement. This study aimed to examine differences between problem and moderate-risk gamblers among Internet and non-Internet gamblers to determine the mechanisms for how Internet gambling may contribute to gambling problems. Australian gamblers (N = 6,682) completed an online survey that included measures of gambling participation, problem gambling severity, and help seeking. Compared with non-Internet gamblers, Internet gamblers were younger, engaged in a greater number of gambling activities, and were more likely to bet on sports. These differences were significantly greater for problem than moderate-risk gamblers. Non-Internet gamblers were more likely to gamble on electronic gaming machines, and a significantly higher proportion of problem gamblers participated in this gambling activity. Non-Internet gamblers were more likely to report health and psychological impacts of problem gambling and having sought help for gambling problems. Internet gamblers who experience gambling-related harms appear to represent a somewhat different group from non-Internet problem and moderate-risk gamblers. This has implications for the development of treatment and prevention programs, which are often based on research that does not cater for differences between subgroups of gamblers.