In a prospective cohort study the authors examined associations between childhood intelligence at age 11 and inflammatory and hemostatic biomarkers in middle age.Participants were 9,377 men and women born in the United Kingdom in March 1958, and whose blood plasma samples at age 45 years were analyzed for levels of C-reactive protein (CRP), D-dimer, fibrinogen, tissue plasminogen activator (t-PA) antigen, and von Willebrand factor (VWF). Sex-adjusted linear regression models tested cognition-blood biomarker associations, with and without adjustment for potential confounding by parental socioeconomic status and potential mediation by cardiovascular disease (CVD) risk factors at midlife. Cognitive tests taken at age 50 enabled the inflammation-cognition association to be tested for reverse causation, by adjusting for age 11 intelligence.Higher childhood intelligence test scores were significantly associated (p < .001) with lower adult levels of CRP (beta coefficient = -0.068), t-PA antigen (β = -0.014), D-dimer (β = -0.011), fibrinogen (β = -0.011), and VWF antigen (β = -0.008). Early life factors including parental socioeconomic status accounted for 24%-44% of these associations, whereas further adjustment for adult CVD risk factors largely attenuated the effects (82%-100%). The significant inverse associations between age 45 biomarker levels and age 50 cognition could be accounted for to a substantial degree by childhood intelligence (50%-100% attenuation).Childhood intelligence is predictive of inflammatory and hemostatic biomarker status at middle age, which may be largely explained by health behaviors. This highlights the need to consider possible bidirectional associations between cognition and inflammation (and hemostasis) in lifecourse models of CVD-related health.