Objective: Health professionals are role models for the community; thus, the oral health condition of the public is shaped potentially by oral self-care attitudes of health professionals. The aim of the present study was to compare dental and medical students' dental health attitudes and behaviour in their pre-clinic stage in Iran. Methods: In 2012, a cross-sectional study was conducted in three dental schools and one medical school in Tehran. A Persian version of HU-DBI (Hiroshima University-Dental Behavioural Inventory) questionnaire was prepared, validated, and distributed among the all pre-clinical students of dental and medical schools at the end of the second year of education through a census method (n = 156). Chi-square test and logistic regression model served for statistical analysis. Results: In total, 144 questionnaires were returned (response rate = 92.3%). Generally, the dental students reported more favourable attitudes and behaviours. The most important differences between medical and dental students were found in four items: not worrying much about visiting the dentist (37.5% vs. 19.3% agreement, respectively, P = 0.01), be bothered by the colour of gums (8.9% vs. 1.1% agreement, respectively, P = 0.02), brushing each of teeth carefully (48.2% vs. 65.9% agreement, respectively, P = 0.03), and using a toothbrush with hard bristles (32.1% vs. 17% agreement, respectively, P = 0.03). Conclusions: Some aspects of oral health attitudes and behaviours among dental and medical students need to be improved. Dental students seem to show better behaviour probably due to their dental education experience.