The 20-item Gamblers’ Beliefs Questionnaire (GBQ) is used to identify cognitive distortions commonly had by gamblers. There is a great need for psychometrically validated instruments for both treatment and research purposes in the field of gambling addiction in Sweden. The purpose of this study was to validate a Swedish translation of the GBQ by assessing internal consistency, convergent validity, known-groups validity, the two-factor structure of the GBQ, and scaling success. The GBQ was translated into Swedish (GBQ-SE) and validated in a sample of 402 Swedish speaking women (47.9%) and men (52.1%) between 18–86 years, representing undergraduates, a working population, and people with current or historical gambling problems. The GBQ-SE showed excellent internal consistency and moderate relationships with instruments of problem gambling severity. We also showed that problem gamblers tend to endorse more gambling related distortions than non-problem gamblers by finding a significantly higher level of cognitive distortions in the problem gambler group. We were not able to confirm the two-factor structure in our sample. When assessing scaling success an overlap for eight of twenty of the items between the subscales was found. We conclude that the GBQ-SE is valid as a general instrument of gambling related cognitive distortions. It can be used to aid in treatment planning with gambling addicted clients, to evaluate treatment outcome, and for research purposes.