The key underlying reason for the rapid aging of the registered nurse (RN) workforce is the declining propensity of young women to become RNs. Unless this trend is reversed, the RN workforce will soon fall well below projected requirements of the health care industry. It is critical that we understand why women are not choosing nursing as a career. Douglas Staiger, David Auerbach and Peter Buerhaus examine this issue using data drawn from the U.S. Bureau of the Census' Current Population Surveys (CPS) and Cooperative Institutional Research Program (CIRP) freshman surveys, which include career plans of college freshmen. The data indicates that the main cause of declining interest in nursing has been the expansion of career opportunities in traditionally male-dominated occupations over the last three decades. Specifically, the data shows that women have largely stopped entering a wide range of traditionally female-dominated occupations, such as nursing or primary school teaching. The data also shows a relative decline in the school grades of women interested in nursing against all other freshman women, suggesting that high academic performers are increasingly interested in professional careers in other fields. This is the third article in a series of four examining changes in the RN workforce. Previous articles addressed aging in the RN workforce as a factor in nurse shortages, and the interplay between the prevalence in associate degree programs and aging in the RN workforce.