OBJECTIVES. A study of pathological gambling in five states provides information needed to address the public health threat that the expanding availability of legalized gambling poses to at-risk groups in the general population. METHODS. Over the course of this project, epidemiological data were collected to determine the prevalence of probable pathological gambling in the general population in each study state and demographic data were collected from pathological gamblers entering treatment programs in each state. RESULTS. Among the states surveyed, the availability of and involvement in gambling differ significantly, as does the prevalence of pathological gambling. Despite these differences, the demographics of pathological gamblers in these states are similar. Like those in the general population, pathological gamblers entering treatment in each state are similar. However, pathological gamblers entering treatment do not represent the full spectrum of individuals in the general population who experience gambling-related problems. CONCLUSIONS. These findings raise a number of issues, including the potential impacts of continued gambling legalization on the overall rate of gambling problems in the general population and on specific at-risk groups, including women, minorities, and children. They thus have implications for policy and program decisions now being made throughout the United States.