Decreased serum TSH levels predict cardiovascular mortality, which could be explained by left ventricular hypertrophy (LVH). The aim of this analysis was to investigate the association between thyroid function and LVH. The population-based Study of Health in Pomerania was conducted in a previously iodine-deficient area. Data of 1510 individuals at least 45 yr of age with echocardiography and without thyroid disorders were analyzed. LVH was defined as a left ventricular mass index (LVMI) exceeding 150 g/m(2) (men) or 120 g/m(2) (women). Overt hyperthyroidism was associated with LVMI (P < 0.01), whereas euthyroid subjects and those with elevated TSH levels did not significantly differ with regard to LVMI. LVH was observed in three (15.0%) subjects with elevated serum TSH levels, in 127 (10.5%) euthyroid persons, in 24 (12.5%) individuals with decreased serum TSH levels, and in four (57.1%) subjects with hyperthyroidism (P < 0.01). Logistic regression analysis identified overt hyperthyroidism as an independent risk factor for LVH (odds ratio, 13.65; 95% confidence interval, 2.83-65.75; P < 0.01). There is an association between thyroid function status, cardiac mass, and LVH. Hyperthyroidism is an independent risk factor for LVH.