BACKGROUND: Overt hypothyroidism is well-known cause of secondary hyperlipidemia and atherosclerosis. However, there have been dissenting reports of abnormalities in serum lipid concentrations in patients with subclinical hypothyroidism (SH). Recently, it has been reported that serum Lp (a) concentration, an independent risk factor of atherosclerosis, was increased in patients with SH. Therefore, we analyzed serum Lp (a) and other lipid concentrations to investigate whether they are increased in patients with SH and the correlation between serum Lp (a) and TSH concentrations. METHODS: We undertook this study in 53 patients with SH (TSH > 6 uiU/ml) and 197 age-and sex-matched healthy control subjects, They had no abnormalities in liver function, BUN, creatinine, fasting blood glucose, urinalysis, and past medical histories. Serum T3, T4, and TSH concentrations were measured by RIA using commercial kits. Serum concentrations of Lp (a), total cholesterol, triglyceride (TG), and HDL cholesterol (HDL-C) were measured by rate nephelometry and enzyme assay, respectively. RESULTS: There were no significant differences of serum Lp (a), total cholesterol, LDL cholesterol, TG, and HDL-C concentrations in 53 patients with SH and 197 control subjects (25.6+-3.8mg/dL vs. 25.4+-1.5mg/dL ; 204.0+-4.2mg/dL vs. 204.0+-2.4mg/dL ; 127.0+-3.9mg/dL vs. 125.0+-2.3 mg/dL ; 133.0+-8.5mg/dL vs. 130.0+-6.0mg/dL ; 50.0+-1.5mg/dL vs. 53.0+-0.9mg/dL). There was no correlation between Lp (a) and TSH concentrations in SH (r=0.12, p>0.05). CONCLUSION: Serum Lp (a) concentration as well as total cholesterol, LDL cholesterol, and TG was not increased in patients with SH. There was no correlation between serum Lp (a) and TSH levels in subclinical hypothyroidism.