OBJECTIVE We prospectively examined whether family socioeconomic status (SES) in childhood is associated with metabolic syndrome (MetS), impaired fasting glucose (IFG), or type 2 diabetes in adulthood. RESEARCH DESIGN AND METHODS The sample comprised 2,250 participants from the longitudinal Cardiovascular Risk in Young Finns Study cohort. Participants were 3–18 years old at baseline (mean age 10.6 years), and they were followed for 31 years. SES was characterized as reported annual income of the family and classified on an 8-point scale. RESULTS For each 1-unit increase in family SES in childhood, the risk for adult MetS decreased (risk ratio [95% confidence interval] 0.94 [0.90–0.98]; P = 0.003) when adjusted for age, sex, childhood cardiometabolic risk factors (lipids, systolic blood pressure, insulin, and BMI), childhood physical activity, and fruit and vegetable consumption. The association remained after adjustment for participants’ own SES in adulthood (0.95 [0.91–0.99]; P = 0.005). A similar association was seen between childhood SES and the risk of having either adult IFG or type 2 diabetes (0.96 [0.92–0.99]; P = 0.01, age and sex adjusted). This association became nonsignificant after adjustment for childhood risk factors (P = 0.08). Of the individual components of MetS, lower SES in childhood predicted large waist circumference (0.96 [0.93–0.99]; P = 0.003) and a high triglycerides concentration (0.96 [0.92–1.00]; P = 0.04) after adjustment for the aforementioned risk factors. CONCLUSIONS Lower SES in childhood may be associated with an increased risk for MetS, IFG, and type 2 diabetes in adulthood. Special attention could be paid to children of low SES families to decrease the prevalence of MetS in adulthood.