Lung cancer diagnosis during emergency hospital admission has been associated with higher early secondary-care costs and lower longer-term costs than outpatient diagnoses. This retrospective cohort study analyses the secondary-care costs of 3274 consecutive patients with lung cancer. Patients diagnosed during emergency admissions incurred greater costs during the first month and had a worse prognosis compared with outpatient diagnoses. In patients who remained alive, costs after the first month were comparable between diagnostic routes. In addition to improving patient experience and outcome, strategies to increase earlier diagnosis may reduce the additional healthcare costs associated with this route to diagnosis.