This study investigates the predictive value of impulsivity traits (as measured by the UPPS-P impulsive behaviour scale) and relevant covariates (sociodemographics, gambling severity, dysphoric mood, other potentially addictive behaviours, and non-verbal intelligence) with regard to treatment dropout and level of adherence to therapy guidelines and instructions in patients with gambling disorder. Sixty-six patients seeking treatment for gambling disorder, and recruited to participate in a larger protocol (G-Brain), were initially assessed in impulsivity traits and relevant covariates in the first six months after admission. Of these, 24 patients dropped out (DO) and 42 patients remained in therapy (NDO) during the subsequent 6-month follow-up period. A multivariate analysis of impulsivity subscales suggested prospective differences between DO and NDO, with affect-driven dimensions (positive and negative urgency) seemingly driving these differences. Among these, only positive urgency independently predicted a slight increase in the drop-out probability. In the NDO group, a higher degree of adherence to therapy was independently predicted by lower sensation-seeking scores and stronger awareness of gambling-related problems. Results suggest the presence of affect-driven impulsivity traits as dropout predictors in patients with gambling disorder. Awareness of gambling-related problems and lower sensation-seeking enhanced compliance with therapeutic guidelines and instructions.