Objective: Clinical stage (c-stage) at diagnosis is the most significant prognostic marker for patients with cancer, where 1- and 5-year survival rates as main landmarks when assessing outcomes. This is a population-based case study of Danish c-stage I lung cancer patients who were considered candidates for curative therapy and then died within 1 year after diagnosis (cases). Cases were identified in the Danish Lung Cancer Register (DLCR), and medical records were used to retrieve treatment details and cause of death (CoD). Our aims were, if possible, to identify and describe clusters of patients, in terms of CoD and treatment modality at risk for an adverse short-term outcome. Results: Patients who died early were more frequently male, older, had squamous-cell histology, were less frequently surgically treated and generally had a higher burden of comorbidity. In terms of CoD, 29% died of lung cancer with distant recurrence (DR) as the most common type of recurrence (55%). Death from co-morbidity occurred for 23%, where the largest proportion (36%) died from another cancer. Nineteen percentage died from treatment complications, with the majority being male (p <.001). The remainder died of unknown or other causes. Conclusions: Lung cancer with DR remains the most common CoD. Identifying and accordingly treating patients at risk for DR could potentially improve outcomes. Further studies of the predominantly male subgroup of patients who die of treatment complications are needed. Death from co-morbidity especially in patients with another cancer is a significant CoD and when assessing the quality of lung cancer care a competing event.