A case-control study of breast cancer was conducted in Hawaii with Japanese and Caucasian women between ages 45 and 74. Each case was matched to one hospital and one neighborhood control. In all, 183 sets of Japanese and 161 sets of Caucasian subjects were interviewed. No statistically significant differences were found between cases and controls in their mean intake of total fat, saturated fat, oleic acid, linoleic acid, animal protein, and cholesterol. Although there was a suggestion that cases consumed more saturated fat and oleic acid than neighborhood controls, the differences were not impressive. Consistent with other case-control studies, the present investigation did not provide strong support for the hypothesis that a high-fat diet is a risk factor for breast cancer. Further work is suggested to clarify the role of diet in determining breast cancer risk.