The Nurses' Health Study has grown from a simple questionnaire-based study initiated in 1976 to a rich resource of information collected over 29 years. Important details about lifestyle have been collected throughout the study and, as the study has progressed, blood samples and DNA from buccal cells have been collected and stored. Tumour samples have also been collected from participants who developed cancer. Through analyses that integrate information from these various sources we are advancing our understanding of the causes of cancer and the potential for prevention.