There is irrefutable evidence that regular participation in physical activity has substantial health benefits, and as such participation in mass community-based sports events should be supported. However, with the promotion of physical activity comes the potential risk of medical complications during an acute exercise session, with this risk varying according to the risk factor profile of an individual and the nature of the event. The demographics of marathon race entrants changed over the past two to three decades, and currently about 50% of runners are older than 40 yr. A consolidated view of previously published research shows that in a marathon with a field of 50,000 runners for example, the medical staff will, on average, encounter a sudden death every 2 to 3 yr, a sudden cardiac arrest every year, 25 runners that present with a serious medical complication requiring specialized management or hospitalization, and 1000 runners that require medical attention. Runners may have several intrinsic risk factors that can predispose them to serious acute cardiovascular or other serious noncardiac medical complications on race day. This intrinsic risk can be exacerbated by several extrinsic risk factors as well. As health care professionals, we are obliged to give the best medical advice to individuals who wish to participate in moderate- and high-intensity endurance activities, and at the same time reduce their risk of a medical complication during exercise. Preliminary data indicate that an online prerace medical screening and targeted educational intervention program can be successfully implemented and is effective in reducing the risk of acute medical complications during a race.