Individuals with gambling problems were identified through use of a 24-hour gambling helpline, and information on the identified problem gambler was obtained with regard to the reported presence or absence of gambling-related illegal behaviors. Data were obtained from 826 helpline callers during the period February 15, 1998, to February 14, 1999. The identified gamblers who reported gambling-related illegal behaviors were more likely to have severe gambling-related problems compared with those gamblers who did not report illegal behaviors. Despite being on average younger, gamblers with acknowledged gambling-related illegal behaviors were more likely to report having problems with multiple forms of gambling, debts to acquaintances, having been suicidal secondary to gambling, having used alcohol or drugs excessively, and having received mental health treatment. Secondary analyses of the subgroup of gamblers with gambling-related illegal behaviors revealed that those with reports of arrest or incarceration secondary to gambling were more likely to have features similar to those described for individuals with antisocial personality disorder, which included being male, unemployed, single, and having problems with excessive drug or alcohol use. In contrast, the gamblers who reported gambling-related illegal behaviors but without arrest or incarceration secondary to gambling were predominantly female and more likely to have reports of problems with non-strategic forms of gambling (e.g., slot machines), owing money to legitimate sources of borrowing, having filed for bankruptcy, and having family problems related to gambling. These findings highlight the importance of assessing the illegal behaviors secondary to gambling when considering the type of treatment needed for persons presenting with gambling problems. 6 tables and 53 references