The dramatic and unexpected increase in life expectancy observed over the past few decades in Western countries is undoubtedly one of the great medicosocial achievements of this century. These gains have principally been made at higher ages and are reflected in the proliferation of centenarians. In France, the estimated number of centenarians was 200 in 1953, around 3,000 at the present time, and 6,000 projected for the end of the century. Similar trends are observed in the United Kingdom; the Royal Secretary sent messages of congratulations on behalf of the Queen to 300 centenarians in 1955 and to 3,300 in 1987. In parallel with these demographic observations, research on centenarians is becoming increasingly widespread with clinical and general population studies now having been conducted in France, Hungary, Japan, Italy, Finland, Denmark, the United States, and China. A database on mortality trends in the oldest old has been established by Vaino Kannisto and Roger Thatcher at the Center for Research on Aging, Odense University Medical School, providing validated data on centenarians from 12 Western European countries and Japan since 1950. Additionally, the Danish centenarian register established by Bernard Jeune contains data on centenarians back to the 1700s.