Dr. Frank Speizer was the founding principle investigator of a population based prospective study of over 120,000 women aged 30-55 (Nurses’ Health Study) that started in 1976 and has continued actively to this date. Although originally designed to study the long term outcomes related to the use of exogenous hormones and contraceptives the study has expanded to assess a number of behavioral, nutritional and other life style risk factors for a wide variety of chronic diseases. Dr. Speizer has carried out other large scale population based studies that have included a number of air pollution and health studies, most notably the Harvard Six City Study, as well as other physiologic and epidemiological studies in healthy and disease population groups. Currently Dr. Speizer is a co investigator in The Former Players Health Study at Harvard University, the largest study of living former National Football League players who are being assessed for potential risks related to their football playing experiences. Chronic diseases in a variety domains including neurocognitive, cardiovascular, muscular skeletal, endocrine, and psycho-social outcomes are being assessed prospective.