AIM: A taxometric study of gambling behavior examines whether it is possible to represent the characteristics of extreme gambling as qualitatively distinct (i.e., taxonic) or as a point along a dimension. METHOD: Analyzes the bets made during a 24-month study period by the 4,595 most involved gamblers among a cohort of 48,114 people using an Internet service to gamble on sporting events. Applies two taxometric procedures (i.e., MAMBAC and MAXCOV) to three indicators of betting behavior: total money lost, total number of bets, and total money wagered. RESULTS: The results fail to provide support for the view that the most involved Internet sports gamblers include a distinct category of gamblers. More research is necessary to clarify the similar features of recreational and extreme gamblers and the dimensions that scientists can use to measure these behaviors. Discusses the implications of these findings for clinical, research, and public policy activities.