Spending on health care in markets with a larger percentage of primary care physicians (PCPs) is lower at any point in time than is true in other markets. The relationship between physician workforce composition and the rate of spending growth is less clear. This analysis of market-level Medicare spending data between 1995 and 2005 reveals that the proportion of PCPs is not associated with spending growth. Additional research is needed before the potential causal impact of PCPs can be fully assessed. However, these findings suggest that changes in the composition of the physician workforce will not be sufficient to address spending growth.