The relationship between life-course body mass index (BMI) trajectories and adult risk for cardiovascular disease (CVD) is poorly described. In a longitudinal cohort, we describe BMI trajectories from early childhood to adulthood and investigate their association with CVD risk factors [Type 2 diabetes mellitus (T2DM), high-risk lipid levels, hypertension, and high carotid intima-media thickness (cIMT)] in adulthood (34-49 years). Six discrete long-term BMI trajectories were identified using latent class growth mixture modelling among 2631 Cardiovascular Risk in Young Finns Study participants (6-49 years): stable normal (55.2%), resolving (1.6%), progressively overweight (33.4%), progressively obese (4.2%), rapidly overweight/obese (4.3%), and persistent increasing overweight/obese (1.2%). Trajectories of worsening or persisting obesity were generally associated with increased risk of CVD outcomes in adulthood (24-49 years) [all risk ratios (RRs) >15, P < 0.05 compared with the stable normal group]. Although residual risk for adult T2DM could not be confirmed [RR = 2.6, 95% confidence interval (CI) = 0.14-8.23], participants who resolved their elevated child BMI had similar risk for dyslipidaemia and hypertension as those never obese or overweight (all RRs close to 1). However, they had significantly higher risk for increased cIMT (RR = 3.37, 95% CI = 1.80-6.39). The long-term BMI trajectories that reach or persist at high levels associate with CVD risk factors in adulthood. Stabilizing BMI in obese adults and resolving elevated child BMI by adulthood might limit and reduce adverse cardiometabolic profiles. However, efforts to prevent child obesity might be most effective to reduce the risk for adult atherosclerosis.