Prior work demonstrated that cognitive-behavioral (CBT) and supportive-experiential (SET) group interventions can reduce dysfunctional fear of progression (FoP) in patients with chronic diseases. In this secondary analysis of a randomized controlled study, we investigated determinants of long-term response to group therapy for FoP. Response to therapy after 12 months was assessed using the Reliable Change Index (RCI). Outcome data were available for 129 patients with cancer and 116 patients with chronic arthritis. 37.9% of the patients in the CBT group and 32.7% of those attending the SET group indicated response to therapy (p=.402). Educational level predicted long-term response to therapy (OR 2.53, 95% CI 1.33-4.81; p=.005). Medical patients with lower education may need additional attention in order to gain long-lasting benefit from brief group psychotherapy. However, this investigation needs to be replicated in a study that includes a broader range of psychological predictors.