Objectives: To determine whether the type of treatment in lung cancer patients affects their quality of life, to examine the impact of stress, gender, age, and side effects on the quality of life, as well as the impact of therapy on certain aspects of functioning. Study Design: Cross-sectional study. Participants and Methods: The study was conducted in the period from January to June 2022 at the Department for Respiratory Diseases “Jordanovac”, University Hospital Centre Zagreb. A total of 162 respondents participated in the research, all of which were lung cancer patients who were receiving treatment with chemotherapy, immunotherapy, targeted therapy or combined therapy after surgery. The study was conducted using the EORTC QLQ-C30 questionnaire, version 3.0. Results: The results have shown that stress significantly affects the quality of life, disrupting daily functioning and social interaction. Gender also affects the quality of life; it is noticeable that men have significantly better emotional and cognitive functioning, as well as their general status, in comparison to women. Age has the greatest influence in the domain of social functioning. The effects of the therapy on physical and psychological activity, but also on emotional and cognitive functioning, as well as the financial abilities of the respondents, were observed. The results show that stress, fatigue, side effects, and other symptoms also affect the quality of life. Conclusion: The type of treatment, as well as the treatment itself, over a two-month period in lung cancer patients affects their quality of life. A better quality of life is confirmed in patients treated with immunotherapy in all spheres of quality of life.