We determined the prevalence of smoking among 320 male medical sciences students (174 studying for a medical degree, 95 a bachelor degree and 51 a associate degree) in Semnan, Islamic Republic of Iran. A self-administrated, anonymous questionnaire was used. The prevalence of smoking was 14.4%; 45.6% of the smokers started smoking between the ages of 18 and 20 years, 43.5% starting at university. There was no significant difference in the prevalence between students undertaking different college degrees and also those having different types of accommodation. However the smoking behaviour of friends and family was significantly correlated with smoking in the students. Smoking amongst medical sciences students, who will become the health professionals of the future, needs to be addressed.