The present study aimed to analyze the efficacy and efficiency of two cognitive-behavioral group treatment programs, as well as to determine which factors predict response to treatment, in a sample of pathological gamblers. We included 194 subjects seeking treatment for pathological gambling at Bellvitge University Hospital. The results indicated that our cognitive-behavioral group treatment was efficacious in most patients. The dropout rate for the total sample was 33.0% and the relapse rate was 24.5%. In addition, we observed statistically significant pre-treatment – post-treatment changes in some measures of psychopathological state and severity of gambling behavior. The risk of dropouts and relapses decreased significantly after the fifth session of therapy. Finally, severity of gambling behavior, high impulsivity, high novelty seeking, and severity of the psychopathological state were identified as factors predicting poor response to treatment. However, persistence seemed to act as a temperamental protective factor for relapse.