Until 100 years ago the epidemiological scenario of human diseases had substantially remained unchanged. The 20th century has been characterized by a fantastic advance in life expectancy and by a shift from infectious to chronic degenerative diseases as prevailing causes of death. As an example of the epidemiological revolution in a developed country, we reconstructed, year by year from 1901 to 2000, the situation in Italy. Reference to the situation in other countries is also made. Both crude and age-adjusted mortality data were made available for males and females. A new turning point became evident in the second half of the 20th century with the decline of mortality for cardiovascular diseases and, more recently, for tumors. This review discusses the roots and rationale for these epidemiological changes. The discoveries made in the area of biomedical sciences, the progress in preventive and curative medicine, and the improvement of hygienic conditions have been so spectacular that 1 million lives are saved every year in Italy as compared with the late 19th century.