For a clear understanding of the inherent changes in mortality with advance in age, it is necessary to observe the experience of generations rather than the cross-section of period experience. In fact, the latter may produce a misleading picture as can be illustrated in the case of tuberculosis. Period experience pointed to a rise in tuberculosis death rates with advance in age, whereas generation experience indicates a decline with aging, The present paper proposes the study of mortality changes of all generations existing at one period to a subsequent period. Some characteristics and trends in the changes in generation mortality of white males and white females since 1900 are discussed. It is pointed out, in particular, that since World War II white males have been experiencing a rapidly increasing rise in generation mortality with the approach of midlife. A comparison of generation mortality changes from 1950 to 1960 among countries of traditionally low mortality shows that only males in the other English-speaking countries may be undergoing the same experience as white males in the United States upon the approach of midlife. It is not evident in the Scandinavian countries and the Netherlands and in the other countries. The reason for these differences is not apparent.