A self-administered diet questionnaire designed for use in a cohort study has been assessed in comparison with a detailed quantitative diet history previously used in and validated for case-control studies. One hundred fifty-eight women aged 40 to 59 were asked to complete the self-administered questionnaire and 123 returned it by mail. Of these women, 50 were interviewed at home using the detailed diet history. Estimates of intake of major nutrients other than fat and fatty acids are comparable from the two methods although in general, estimated intake from the self-administered questionnaire was higher than the diet history. The difference in intake of fat and fatty acids was largely but not completely accounted for by differences in amounts of added fat recorded. It is concluded that when applied to large numbers of women in a cohort study, the self-administered questionnaire is feasible to administer and will be sufficiently accurate in estimating nutrient intake as compared to estimates from a detailed, interview-type diet history.