This research tested if decision making while gambling was predicted by gambling passion. Casino patrons (n = 199) recruited from casino foyers completed questionnaires to assess levels of harmonious and obsessive passion for gambling (Vallerand, 2015) and a computerized version of the Iowa Gambling Task (IGT) to assess decision making in a simulated gambling situation. In support of our hypothesis, obsessive (but not harmonious) passion for gambling predicted worse IGT performance: Over the course of the IGT, obsessive passion predicted a greater proportion of selections from disadvantageous compared to advantageous decks of cards, less imaginary money remaining at the end, and, as shown by growth curve modeling, a dampened rate of change in IGT performance. These results demonstrate that the quality of one’s passion predicts decision making in gambling, an effect that has substantial implications for psychological and financial well-being. (PsycINFO Database Record (c) 2018 APA, all rights reserved)