This study analyzed the outcome predictors of an Internet-delivered cognitive behavior therapy (ICBT) for problem gambling, examining users’ socio-economic profile and gambling behavior. Being males and employed, the fact of playing and to have gambling problems for less than a year, preference for non strategy-based games, and high frequency of playing were found to be predictors of therapy dropout. The findings from this study, though preliminary, suggest that certain patients’ socio-economic characteristics and gambling behavior may have a bearing on the success or failure of an ICBT and that there is a need to adapt the therapy for those individuals at risk. In fact, detect at an early stage of the therapeutic relationship those patients with a greater propensity to dropout may allow the implementation of appropriate and customized approaches to reduce the difficulties to follow and complete a therapy.