The Boston Nurses' Health Study is a prospective cohort study of 121,700 female registered nurses followed up since 1976 by means of biennial questionnaires. The subjects for this paper are those cohort members diagnosed with invasive breast cancer between 1976 and 1990 who provided adequate medical and dietary information. Follow-up was until June 1994, or death, whichever occurred first. Diet was assessed by means of food frequency questionnaires, and the index diet was taken to be that completed most closely after the diagnosis of breast cancer. Aspects of diet such as nutrients and foods, were then assessed for their relation with time-to-death from any cause and time-to-death from breast cancer. Results were adjusted by measured covariates, including tumour size and grade, and stage of disease.