The dental profession has a high risk of hepatitis B virus (HBV) contamination and can play a crucial role in controlling HBV cross-contamination. In this cross-sectional study we used unique methods to assess Tehran dentists' knowledge, attitude and behaviour regarding HBV. Two simulated HBV-positive patients visited 300 general/specialist dentists in their offices and recorded dentists' willingness to treat them. Later, the dentists were interviewed regarding their knowledge about hepatitis B and attitude to HBV-positive patients. The mean knowledge score of dentists was 14.3 (SD 6.9) out of 44 and the mean attitude score was 20.0 (SD 3.6) out of 39. A majority of dentists (55.6%) were willing to treat a patient with HBV, unconditionally or with conditions. Some individual attitude items correlated with knowledge items concerning transmission of the virus and its prevention. Dentists' willingness to treat patients did not correlate with knowledge or attitude, except for the attitude item on concern about becoming infected.