<p>Cystic fibrosis presents an inherited disease, which increases the vulnerability of the patients and their families. The mental burden of cystic fibrosis is a given. Evidence-based psychotherapies ought to be an integral part of cystic fibrosis management. This study focuses on the effectiveness of the implementation of an online group cognitive behavioral psychotherapy in Greek cystic fibrosis patients and caregivers within the Hellenic Cystic Fibrosis Association. 39 people participated in the initial evaluation. Two therapy groups-20 individuals (12 patients and 8 caregivers)-took part in this study. A test battery assessing psychopathology, social skills, functional outcome, and recovery was given before and after the therapy. T-paired tests and effect sizes were calculated. Pearson correlation coefficients were computed. Cystic fibrosis patients showed statistically significant results in psychopathology, functioning, and recovery. The overall treatment effect size was 0.65. Caregivers had statistically significant results in psychopathology, social skills, and recovery. The overall treatment effect size was 0.44. This study underpins evidence for the effectiveness of the online group cognitive behavioral psychotherapy in the Hellenic Cystic Fibrosis Association. Advantages and disadvantages are discussed. Further research is needed.</p>