BACKGROUND: There is concern that antioxidant supplement use during chemotherapy and radiation therapy may decrease treatment effects, yet the effects of such supplements on recurrence and survival are largely unknown. METHODS: The authors prospectively examined the associations between antioxidant use after breast cancer (BC) diagnosis and BC outcomes in 2264 women in the Life After Cancer Epidemiology (LACE) cohort. The cohort included women who were diagnosed with early stage, primary BC from 1997 to 2000 who enrolled, on average, 2 years postdiagnosis. Baseline data were collected on antioxidant supplement use since diagnosis and other factors. BC recurrence and mortality were ascertained, and hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using delayed entry Cox proportional hazards models. All tests of statistical significance were 2-sided. RESULTS: Antioxidant supplement use after diagnosis was reported by 81% of women. Among antioxidant users, frequent use of vitamin C and vitamin E was associated with a decreased risk of BC recurrence (vitamin C: HR, 0.73; 95% CI, 0.55-0.97; vitamin E: HR, 0.71; 95% CI, 0.54-0.94); and vitamin E use was associated with a decreased risk of all-cause mortality (HR, 0.76; 95% CI, 0.58-1.00). Conversely, frequent use of combination carotenoids was associated with increased risk of death from BC (HR, 2.07; 95% CI, 1.21-3.56) and all-cause mortality (HR, 1.75; 95% CI, 1.13-2.71). CONCLUSIONS: Frequent use of vitamin C and vitamin E in the period after BC diagnosis was associated with a decreased likelihood of recurrence, whereas frequent use of combination carotenoids was associated with increased mortality. The effects of antioxidant supplement use after diagnosis likely differ by type of antioxidant. Cancer 2011. (c) 2011 American Cancer Society.