Several pubertal and reproductive events are well established risk factors for breast cancer. Age maximum height attained is an understudied potential breast cancer risk factor that may affect risk through mechanisms different from those of other pubertal and reproductive events. We assessed the relationships between different pubertal/reproductive events and risk of different types of breast cancer in a prospective cohort of 27,536 women. Women were recruited between 2000 and 2002 and completed a mailed questionnaire. As of 2005, 585 women were diagnosed with breast cancer. Using a Cox proportional hazards model, women who reached their maximum height at <or=12 years of age had a 1.4-fold [95% confidence interval (95% CI), 1.0-1.8] increased risk of breast cancer compared with women who reached their maximum height at >or=17 years of age (P(trend) = 0.04). This association was primarily limited to more aggressive tumors, specifically those that were estrogen receptor-negative (hazard ratio, 1.9; 95% CI, 1.0-3.9) and diagnosed at a regional or distant stage (hazard ratio, 1.8; 95% CI, 1.0-3.1). There was no difference in the relation of age at menarche with breast cancer by tumor stage, whereas late age at first full-term pregnancy primarily increased risks of less-aggressive disease, including lobular, estrogen receptor-positive, and localized stage tumors. Age at maximum height seems to be an independent risk factor for breast cancer that is more strongly associated with relatively aggressive tumors that have a poorer prognosis compared with the types of tumors that are associated with ages at menarche and first full-term birth.