The World Health Organization's 2009 report on the world's tobacco epidemic predicts that, unchecked, tobacco use will kill a billion people in this century. Oncologists have a special professional role to play in combating this epidemic. Based on two views of professionalism, this editorial argues that oncologists have three duties. First, oncologists should be role models. They should not smoke themselves and urge their colleagues to do the same. Second, oncologists must strongly advise their own patients to stop smoking and advocate for tobacco-free environments in their patients' communities. Third, oncologists have duties to their international colleagues. They should share their experience in combating tobacco use with them, encourage and assist them to quit smoking, and help them advocate for smoke-free environments. Further, oncologists should work to ratify the Framework Convention on Tobacco Control in their own country.