To investigate the association of number of siblings with preclinical cardiovascular disease (CVD) markers in adulthood. The sample comprised 2776 participants (54 % female) from the Cardiovascular Risk in Young Finns Study who had CVD risk factor data measured in childhood in 1980 (aged 3–18 years) and markers of preclinical CVD measured in adulthood. Echocardiography was performed in 2011, and carotid intima-media thickness, carotid distensibility, brachial flow-mediated dilatation, and arterial pulse wave velocity were measured in 2001 or 2007. The association between the number of siblings and preclinical CVD was assessed using generalized linear and logistic regression models. Analyses were stratified by sex as associations differed between sexes. Women with 1 sibling had lower E/e’-ratio (4.9, [95%CI 4.8–5.0]) in echocardiography compared with those without siblings (5.1[4.9–5.2]) and those with ≥2 more siblings (5.1[5.0–5.2]) (P for trend 0.01). Men without siblings had the lowest E/A-ratio (1.4[1.3–1.5]) compared with those with 1 sibling (1.5[1.5–1.5]), or ≥2 siblings (1.5[1.5–1.5]) (P for trend 0.01). Women without siblings had highest left ventricular ejection fraction (59.2 %[58.6–59.7 %]) compared with those with 1 sibling (59.1 %[58.8–59.4 %]), or ≥2 siblings (58.4 %[58.1–58.8 %])(P for trend 0.01). In women, brachial flow-mediated dilatation, a measure of endothelial function, was the lowest among participants with ≥2 siblings (9.4 %[9.0–9.8 %]) compared with those with 1 sibling (10.0 %[9.6–10.3 %]) and those without siblings (10.4 %[9.7–11.0 %])(P for trend 0.03). We observed that number of siblings may be associated with increased risk of heart failure in women. As the associations were somewhat inconsistent in males and females, further research is warranted.