CONTEXT AND OBJECTIVE: Lung cancer is the commonest malignant tumor and is increasing in incidence by 2% a year. In 90% of diagnosed cases, it is associated with tobacco product consumption. It is the greatest cause of mortality among cancer types in Brazil. Knowledge of patients psychological representations is needed for evaluating treatments and educating patients. The aim here was to interpret how smokers with lung cancer interpret the possible causes of their illness and to understand their perceptions regarding cigarette use. DESIGN AND SETTING: Clinical-qualitative study (exploratory, non-experimental) at the Pulmonary Disease Service, General Hospital, Universidade Estadual de Campinas. METHODS: An intentional small sample of cancer inpatients was recruited. The group was closed with 11 subjects, following attainment of data saturation from interviews. These interviews were semi-directed, with in-depth open-ended questions on interviewees observations, applied in a confidential setting using a tape recorder. Interviewees responses were categorized using qualitative content analysis and the results were assessed using interdisciplinary theoretical concepts, particularly from medical psychology. RESULTS: Six males and five females aged between 46 and 68 years who presented diverse clinical conditions were interviewed. CONCLUSIONS: A broader approach towards the psychological comprehension of such patients is needed, considering that cigarette consumption involves conscious and unconscious motivations, sociocultural and educational factors, the glamour of tobacco advertising, and problems with psychophysical dependence. Such an approach would avoid the perception among patients that the healthcare team are "inquisitors". This would lead to better adherence to treatment and better quality of life.