Teaching about tobacco and related diseases is essential in the undergraduate medical course in order for students to gain knowledge about smoking and how to intervene with patients who smoke. The objective of the study was to assess students' smoking-related behaviour, knowledge and attitudes towards tobacco, and perceptions of their future role as doctors. Data were collected from two consecutive years of year 1 and year 5 medical students at the University of New South Wales, Sydney. A total of 594 (79%) of students across the 2 years completed the survey: 90% of year 1 students, and 69% of year 5 students. The daily smoking rate among the total medical students was 2.9%: 11.8% in year 1 (2.3% daily, 9.5% occasional) and 13.7% in year 5 (3.3% daily, 10.4% occasional). There were significantly more male than female smokers in year 5 (P < 0.05). The overall smoking rates for males in years 1 and 5 were 12.4% and 19.3%, and the smoking rates for females were 11.2% and 8%. Knowledge about the causal role of tobacco in the development of specific diseases improved significantly from year 1 to year 5 (P < 0.001). Nevertheless, in year 5 there remained a lack of knowledge about the relationship of smoking and some diseases. Fifty-seven per cent of students thought that their current knowledge was sufficient to counsel smokers, with year 5 students (89%) being far more positive than year 1 students (34%) (P < 0.001). Teaching medical students about smoking-related diseases and a patient-centred smoking cessation intervention results in an increase in knowledge, as well as positive perceptions about their future role in intervening with smokers.