For over two centuries, U.S. vital statistics routinely have been stratified by age, sex, and race, but not by social class. The usual explanation is that U.S. government officials have not considered social class relevant to health. During the first third of the 20th century, however, questions of socio-economic inequalities in morbidity and mortality ranked high on the agenda of federal and other public health agencies, and routine reporting of U.S. vital statistics and health survey data by socioeconomic measures was nearly institutionalized. This history has largely been lost. In this article, the authors focus on the period from 1900 to 1950 and examine how public health researchers and agencies conceptualized and analyzed socioeconomic inequalities in health. Highlights include production, for 1930, of the first U.S. national death rates stratified by social class, in work sponsored by the National Tuberculosis Association and Bureau of the Census, and the Public Health Service's 1935-1936 National Health Survey, which reported morbidity data stratified by socioeconomic measures. Efforts like these were cut short by the onset of World War II and their legacy erased by the Cold War. Recovering this rich history can help inform current debates about collecting and evaluating data on social inequalities in health.