Increasing evidence supports the importance of socioeconomic factors in the development of atherosclerotic cardiovascular disease. However, the association of childhood socioeconomic status (SES) with arterial stiffness in adulthood has not been reported. Our aim was to determine whether higher childhood family-level SES is associated with lower arterial stiffness in adulthood. The analyses were performed using data gathered within the longitudinal Young Finns Study. The sample comprised 2566 participants who had data concerning family SES at ages 3 to 18 years in 1980 and arterial pulse wave velocity and carotid artery distensibility measured 21 or 27 years later in adulthood. Higher family SES in childhood was associated with lower arterial stiffness in adulthood; carotid artery distensibility being higher ( β value±SE, 0.029±0.0089%/10 mm Hg; P =0.001) and pulse wave velocity lower ( β value±SE, −0.062±0.022 m/s; P =0.006) among those with higher family SES in a multivariable analysis adjusted with age, sex, and conventional childhood cardiometabolic risk factors. The association remained significant after further adjustment for participant’s SES in adulthood ( β value±SE, 0.026±0.010%/10 mm Hg; P =0.01 for carotid artery distensibility and β value±SE, −0.048±0.023 m/s; P =0.04 for pulse wave velocity) but attenuated after adjustment for adulthood cardiometabolic risk factors ( β value±SE, 0.015±0.008%/10 mm Hg; P =0.08 for carotid artery distensibility and β value±SE, −0.019±0.02 m/s; P =0.38 for pulse wave velocity). In conclusion, we observed an association between higher family SES in childhood and lower arterial stiffness in adulthood. Our findings suggest that special attention could be paid to children from low SES families to prevent cardiometabolic diseases primordially.