BACKGROUND Cardiovascular disease and type 2 diabetes are two of the most common public health diseases, and up to 80 % of the cases may be prevented by lifestyle modification. The physiological effects of lifestyle-focused treatment are relatively well studied, but how patients actually experience such treatments is still rather unclear. PURPOSE The aim of this study was to explore how patients experience lifestyle-focused group treatment in primary and secondary prevention of cardiovascular disease and type 2 diabetes. METHOD Qualitative interviews were conducted with 19 patients attending lifestyle-focused group treatment based on social cognitive theory at a behavioral medicine clinic in northern Sweden. The interviews were transcribed verbatim and analyzed according to Malterud's systematic text condensation. RESULTS The study shows that patients participating in this kind of group-based lifestyle treatment went through a process of self-development which deepened their understanding of own responsibility for health and improved their skills in finding support in others. The process could be tracked through three different themes (the holistic view, personal responsibility, and group treatment) which together reflected the most essential parts of the informants' experience and showed the patient as an active decision maker struggling to adopt the principles of behavioral change. CONCLUSION Lifestyle-focused group treatment, based on social cognitive theory, was shown to stimulate different components that strengthen patients' self-efficacy for long-term behavioral change.