In October 1951, the researchers wrote to all registered physicians in the United Kingdom, and obtained responses in two-thirds, 40,701 of them.
The respondents were stratified into decade of birth, sex and their cause-specific mortality, as well as general physical health and current smoking habits, followed up in further questionnaires in 1957, 1966, 1971, 1978, 1991 and finally in 2001.