Objective. The objective of this study was to describe the impact on patient-reported outcomes of introducing Shared Decision Making (SDM) and a Patient Decision Aid (PtDA) in the initial process of lung cancer diagnostics. Methods. We conducted a prospective cohort study, where a control cohort was consulted according to usual clinical practice. After introducing SDM through a PtDA and training of the staff, the SDM cohort was enrolled in the study. All patients completed four questionnaires: the Decisional Conflict Scale (DCS) before and after the consultation, the CollaboRATE scale after the consultation, and the Decision Regret Scale (DRS). Results. Patients exposed to SDM and a PtDA had significantly improved DCS scores after the consultation compared to the control group (a difference of 10.26, p = 0.0128) and significantly lower DRS scores (a difference of 8.98, p = 0.0197). Of the 82 control patients and 52 SDM patients 29% and 54%, respectively, gave the maximum score on the CollaboRATE scale (Pearson's chi 2 8.0946, p = 0.004). Conclusion. The use of SDM and a PtDA had significant positive impact on patient-reported outcomes. Practice Implications. Our results may encourage the increased uptake of SDM in the initial process of lung cancer diagnostics. 2. Methods 2.1 Design. We designed a prospective cohort study comparing an unexposed cohort with an exposed cohort. The study included two phases, a control baseline phase followed by a SDM phase. The intervention was the introduction of SDM and a PtDA, specifically developed for this clinical setting. The staff was trained in conducting SDM and using the PtDA after the control baseline and just before the SDM phase. The training took place as 8-hour courses with 8-10 participants, doctors and nurses together. The main focus was on SDM principles, secondarily on the PtDA. During the SDM phase, new staff was training one-by-one by the study nurse for half an hour. After this introduction, SDM and the PtDA were tested in the daily clinical work at the Lung Cancer Organization during the SDM phase. 2.2 Setting. The fast-track Lung Cancer Organization at Vejle Hospital, Denmark, is a high volume center certified by the Organization of European Cancer with a population basis of around 600,000 people. Every year, 1,600 patients are referred to the organization on suspicion of lung cancer and malignancy is confirmed in around 450. The Division of Respiratory Medicine coordinates the fast-track Lung Cancer Organization, which works closely together with many other specialties at the hospital, including radiology, nuclear medicine, oncology, radiation therapy, and pathology. On a yearly basis around 1,000 bronchoscopies, 600 endoscopic ultrasound examinations of intrathoracic lymph nodes, 1,000 CT guided lung biopsies, and 1,500 PET-CT scans are conducted on suspicion of lung cancer. The Center for Shared Decision Making at Vejle Hospital was established in 2014 and other PtDAs have been developed, clinically tested, and evaluated there, previously mostly in cooper...