Height and body size in childhood and young adulthood have been consistently associated with breast cancer risk; whether associations differ across molecular subtypes is unclear. In a pooled analysis of the Nurses’ Health Studies we prospectively examined the association of four exposures: height, body mass index (BMI) at age 18, childhood and adolescent somatotypes, with breast cancer risk according to molecular subtypes defined by immunohistochemical markers. We used multivariable-adjusted Cox proportional hazards regression to estimate hazard ratios (HR) and 95% confidence intervals (CI).We identified 2983 luminal A, 1281 luminal B, 318 HER2-enriched, 408 basal-like and 128 unclassified tumors. Height was positively associated with all subtypes (p-heterogeneity=0.78). BMI at age 18 (p-heterogeneity=0.001), childhood (p-heterogeneity=0.51) and adolescent somatotype (p-heterogeneity=0.046) were inversely associated, but with differences in magnitude of association. BMI at age 18 of ≥25 kg/m2 (compared to 20-21.9 kg/m2) was associated with a 52% decreased risk of HER2-enriched (HR: 0.48, 95%CI: 0.26-0.91; p-trend <0.0001) and 39% reduced risk of basal-like tumors (HR: 0.61, 95% CI: 0.36-1.02; p-trend=0.008). Compared to the lowest category, women in the highest adolescent body size category were 71% less likely to develop HER2-enriched (HR: 0.29, 95%CI: 0.10-0.85; p-trend=0.0005) and 60% less likely to develop basal-like (HR: 0.40, 95%CI: 0.17-0.95; p-trend=0.0008). Height was positively associated with risk of all breast cancer molecular subtypes. BMI at age 18 and childhood and adolescent were inversely associated with risk of most breast cancer molecular subtypes with somewhat stronger associations with HER2-enriched and basal-like subtypes.