Dietary choline and betaine deficiencies decrease S-adenosylmethionine (SAM) concentrations which results in DNA hypomethylation. DNA hypomethylation may result in increased expression of oncogenes and an increased risk of DNA mutations, thus providing a basis for primary tumor growth and metastasis. Associations between DNA hypomethylation and colorectal, breast, and lung cancers have been reported. Betaine and choline intake may also be associated with coronary heart disease (CHD) and ischemic stroke risk through an atherogenic homocysteine methylation pathway. No studies have examined the relationship between these outcomes and habitual dietary choline and betaine intake. Until recently there were insufficient analytical data to estimate choline intake in populations. We will estimate the association between dietary total choline and betaine intake and the risk of cancer (colorectal; lung; invasive breast) and atherothrombotic (CHD; ischemic stroke) endpoints in the Women’s Health Initiative (WHI) Observational Study and the WHI Dietary Modification trial data collected over 8-12 years of follow-up. Food consumption data, quantified from the WHI Food Frequency Questionnaire will be converted into estimates of daily intake of total choline and betaine using the United States Department of Agriculture conversion values. If confirmed, the hypothesized association with chronic disease endpoints would suggest targets for primary prevention.