BACKGROUND: Lung cancer is the commonest cause of cancer in Scotland and is usually advanced at diagnosis. Median time between symptom onset and consultation is 14 weeks, so an intervention to prompt earlier presentation could support earlier diagnosis and enable curative treatment in more cases. AIM: To develop and optimise an intervention to reduce the time between onset and first consultation with symptoms that might indicate lung cancer. DESIGN AND SETTING: Iterative development of complex healthcare intervention according to the MRC Framework conducted in Northeast Scotland. METHOD: The study produced a complex intervention to promote early presentation of lung cancer symptoms. An expert multidisciplinary group developed the first draft of the intervention based on theory and existing evidence. This was refined following focus groups with health professionals and high-risk patients. RESULTS: First draft intervention components included: information communicated persuasively, demonstrations of early consultation and its benefits, behaviour change techniques, and involvement of spouses/partners. Focus groups identified patient engagement, achieving behavioural change, and conflict at the patient-general practice interface as challenges and measures were incorporated to tackle these. Final intervention delivery included a detailed self-help manual and extended consultation with a trained research nurse at which specific action plans were devised. CONCLUSION: The study has developed an intervention that appeals to patients and health professionals and has theoretical potential for benefit. Now it requires evaluation.