Adult height has been positively associated with breast cancer risk in epidemiologic studies, and recent evidence suggests that the timing and rate of growth may also influence risk. We examined both adult height and age at attained height, an indicator of the timing of the pubertal growth spurt, in relation to incidence of premenopausal breast cancer in the Nurses' Health Study II. Participants were 108,829 premenopausal women who reported their height in 1989; of these, 37,572 provided information on their age at attained height on a later supplementary questionnaire. During 12 years of follow-up, 1,041 cases of invasive breast cancer were identified (402 with age at attained height). Cox proportional hazards models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). Adult height was positively associated with breast cancer incidence; the multivariate RR for participants 1.75 m or taller compared to those shorter than 1.60 m was 1.57 (95% CI: 1.23-2.01, p trend < 0.0001), and each 5-cm increment corresponded to an 11% increase in risk (95% CI: 6-17%). There was no overall association for age at attained height, however, with a multivariate RR of 0.96 (95% CI: 0.66-1.39) for women who attained their maximum height at age 18 or older compared to those who reached it before age 14 (p trend = 0.65). These results confirm previous findings that taller adult height is associated with increased risk of premenopausal breast cancer but do not provide evidence that age at attained height is related to risk.