This study was performed to ascertain whether a relationship exists between thyroid function and blood pressure in school-aged Chinese subjects without overt thyroid disease. A cross-sectional survey of 880 subjects (541 females and 339 males) aged 7-18 years in Bengbu, Anhui province was conducted. The investigation, which was based on a stratified random cluster sampling method, included a questionnaire and measurements of blood pressure, height, and body weight. Fasting blood samples were taken for measurements of thyroid-stimulating hormone (TSH), free 3,5,3'-triiodothyronine (FT(3)) and free thyroxine (FT(4)). Serum TSH and FT(3) were positively correlated with systolic and diastolic blood pressure Z scores (SBP-Z and DBP-Z) even after adjusting for body mass index (BMI) (P < 0.05) but no correlation was observed between FT(4) and SBP-Z or DBP-Z after comparable adjustments (P > 0.05). SBP-Z and DBP-Z in subjects with subclinical hypothyroidism were significant higher than in euthyroid subjects (P < 0.05). Both SBP-Z and DBP-Z increased linearly with TSH concentration in boys after adjusting BMI (P < 0.05); however, a similar linear trend was not observed in girls. Our findings support the hypothesis that elevated TSH and FT(3) concentrations increase blood pressure in school-aged Chinese subjects without overt thyroid disease; this increase may be even more significant in boys.