To examine the factors responsible for the rise in health- care spending in the United States over the past 15 years. Nationally representative survey data from 1987 and 2003 were used to examine the top medical conditions accounting for the rise in spending. I also estimate how much of the rise is traced to rising treated disease prevalence and rising spending per case. The study finds most of the rise in spending is linked to rising rates of treated disease prevalence. The rise in prevalence is associated with the doubling of obesity in the US and changes in clinical thresholds for treating asymptomatic patients with certain cardiovascular risk factors. Most of the policy solutions offered in the US to slow the growth in spending do not address the fundamental factors accounting for spending growth. More aggressive efforts for slowing the growth in obesity among adults and children should be centre-stage in the efforts to slow the rise in health-care spending.