This review deals with the published literature to date while examining the relationship between online gambling, mental health problems, and substance use. Online gambling, particularly problematic gambling online, was found to be associated with poor mental health and use of various substances. Recent preliminary evidence also suggests that online gamblers may be at a greater risk of some substance use and mental health problems, relative to nononline gamblers. However, many of the reviewed studies were limited by investigation of online gambling behaviors only; these samples may have inadvertently comprised individuals who engage in both online and nononline gambling. Future research is required to address these limitations.