We assessed the relation between beta-carotene consumption at various times in life and breast cancer risk by conducting a case-control study nested within a population-based cohort of women screened for breast cancer in Sweden. We conducted a telephone interview with 273 incident breast cancer cases and 371 controls about their diet at various ages throughout their lifetime. Controls were frequency matched to cases on age, month and year of mammography, and county of residence. We used unconditional logistic regression to measure the association between beta-carotene intake and breast cancer risk while adjusting for total energy intake, recency of intake, and the matching variables. Women were at lower risk with increasing levels of reported intake of beta-carotene. This pattern of association between breast cancer and beta-carotene intake was similar at various times before screening. These findings indicate that although diets high in beta-carotene may be associated with lower breast cancer risk, there does not seem to be evidence of a critical time period during which such diets are more relevant. (Epidemiology 1999;10:49–53)