Details of design and data collection used in the HPFS and the NHS II have been previously published.27- 29 In brief, the HPFS was started in 1986 when 51,529 US male health professionals aged 40 to 75 years responded to a mailed questionnaire. The NHS II began in 1989 when 116,686 US female registered nurses aged 25 to 42 years returned a mailed questionnaire. At the time of enrollment, members of both cohorts provided a detailed medical history, including diagnosed diseases, medication, and information on lifestyle factors including smoking. Information on dietary intake and physical activity was also obtained from a semiquantitative food frequency questionnaire30 and a standardized physical activity questionnaire, respectively.31 Biennial questionnaires were mailed to participants to update newly diagnosed disease. Questions about the diagnosis of pneumonia were included in the HPFS questionnaires beginning in 1990 and in the NHS II since 1991; therefore, the baseline was considered to be the date of return of the questionnaire in 1990 or 1991, respectively. Among 39,044 men and 95,237 women who responded to the baseline questionnaire, we excluded participants in whom pneumonia occurred during a hospitalization (14 men, 19 women), those in whom the diagnosis of pneumonia was not identified by medical records (246 men) or by the supplementary questionnaire (50 women), those in whom the reported pneumonia was diagnosed before the beginning of the study (338 men, 59 women), or those who did not respond to questions on body weight and physical activity (5320 men, 10,379 women). Among women, we excluded participants who reported on a supplementary questionnaire that their diagnosis of pneumonia was probable or possible (137 women) and included only women who reported a definite diagnosis. At baseline, we also excluded 6697 men (asthma, 17%; cardiovascular disease, 42%; cancer, 20%; diabetes, 21%) and 6531 women (asthma, 74%; cardiovascular disease, 6%; cancer, 8%; diabetes, 12%) to avoid confounding by diseases that could affect associations between smoking, body weight, and exercise, as well as alcohol intake and pneumonia incidence. The remaining 26,429 men and 78,062 women were eligible for analysis.