Over time, trends in modifiable, behavioral risk factors, like smoking and obesity, can have a significant effect on population wide life expectancy. Previous estimates suggest that obesity accounts for 5-15% and smoking for 18% of all deaths in the U.S. Over the past 15 years, smoking rates have decreased by about 20%, but obesity rates have increased by 48%. By projecting these trends out into the future for 15 years, these investigators predict that for an average 18 year old the decreased prevalence of smoking will lead to an increase in life expectancy of 0.31 years (quality adjusted life expectancy 0.41 years), but the increased prevalence of obesity will lead to a decrease in life expectancy by 1.02 years (quality adjusted life expectancy of 1.31 years). Overall, the benefit of smoking cessation is expected to be overwhelmed by the increased risk associated with increasing obesity rates; overall net life expectancy is projected to decrease by 0.71 years (quality adjusted life expectancy of 0.91 years). In a purely hypothetical scenario, if we could completely eliminate both smoking and obesity, by 2020 average life expectancy would increase by 3.76 years (quality adjusted life expectancy of 5.16 years). These are humbling projections that call for increased public health action, which should be focused on continuing the current positive trends in smoking cessation and doing everything possible to slow the epidemic of obesity. Given the inherent difficulty in decreasing the incidence of obesity, we also need to intensify our efforts to treat the metabolic consequences of obesity to help attenuate the attributable risk, particularly the cardiovascular risk, associated with obesity. Michael J. Bloch, M.D.