Doctors are well positioned to provide physical activity (PA) counselling to patients. They are a respected source of health-related information and can provide continuing preventive counselling feedback and follow-up; they may have ethical obligations to prescribe PA. Several barriers to PA counselling exist, including insufficient training and motivation of doctors and improvable, personal PA habits. Rates of exercise counselling by doctors remain low; only 34% of US adults report exercise counselling at their last medical visit. In view of this gap, one of the US health objectives for 2010 is increasing the proportion of patients appropriately counselled about health behaviours, including exercise/PA. Research shows that clinical providers who themselves act on the advice they give provide better counselling and motivation of their patients to adopt such health advice. In summary, there is compelling evidence that the health of doctors matters and that doctors' own PA practices influence their clinical attitudes towards PA. Medical schools need to increase the proportion of students adopting and maintaining regular PA habits to increase the rates and quality of future PA counselling delivered by doctors.