The authors studied 439 postmenopausal breast cancer cases, identified in hospitals throughout western New York, with an interview schedule that considered frequency and amount ingested of 172 foods and provided data for an estimate of total calories ingested. These were compared with age-matched controls comprising a random sample of the same communities as the cases. The extensive interviews, requiring 2.0 hours on average to administer, also covered alcohol ingestion, Quetelet index, and a wide variety of reproductive factors. The authors found, as have most investigators over the past 25 years, that risk increased with increases in age at first pregnancy, decreased with increases in numbers of children and pregnancies, and increased in those with history of benign breast disease and in those with female relatives previously affected with breast cancer. Risk adjusted for potential confounders was highest among women with the lowest ingestion of carotene or a substance correlated with its ingestion. Risk was not associated with retinol ingestion. It increased with increases in Quetelet index. Fat intake, whether studied in terms of quantity or the proportion of total calories derived from fat, was not associated with risk of breast cancer. Our analyses of these factors were adjusted for age, education, and the reproductive history traits described above.