Background - Lung cancer is the second most common cancer diagnosed in the UK after breast cancer. Around 41,000 people were diagnosed with lung cancer in the UK in 2008 (or 112 people every day). Patients with symptoms suggestive of lung cancer usually present to their GP first who operate a gatekeeping role for referrals into secondary care. Aims - This study aimed to identify factors influencing GPs in the recognition and referral of patients with suspected lung cancer and to identify potential modifiable factors in order to develop interventions in the future to enable GPs to recognise and refer patients with lung cancer appropriately. Methods - Thirty six in-depth interviews with GPs were conducted across Hull, East Riding of Yorkshire, North East Lincolnshire and North Yorkshire. The interviews were in two parts: first, a number of clinical case scenarios were presented to the participants and think aloud methodology applied to establish insights into GPs cognitive processes in decision making. The second part was an in-depth exploration of the process of recognition and referral of patients with suspected lung cancer symptoms. Thematic analysis was used for the development of key themes. Findings - Data analysis identified four key themes from the data: [1] the ways in which GPs make decisions and in particular how they deal with challenging or unusual presentations, [2] understanding the differences in how GPs run their practices and how this may impact upon decision making, [3] the complexity of general practice and [4] the pressures faced by general practitioners. The findings from the think aloud method emphasised the focus participants placed on symptoms, context and patient factors in the development of a clinical hypothesis. It was then a process of seeking to prove or disprove a hypothesis by working through a list of differential diagnoses and complexity within the time constraints and context of the consultation. The open-ended interviews added reliability by corroborating some of the think aloud findings regarding knowledge and compliance of lung cancer guidelines but also introduced a broader perspective about practice factors involving internal organisational culture, structures and processes not mentioned in think aloud but which may influence participants in consultations. Conclusion - The study has learned that the recognition and referral of lung cancer is complex. The research findings highlight a range of factors which help understand what makes it easier to recognise and refer lung cancer and also what are the barriers to recognising and referring lung cancer in general practice and how this may potentially impact on GP consultations.