Objectives: Though overt thyroid dysfunction is well recognized to affect serum lipid profiles and obesity, there are conflicting reports on the effect of subclinical hypothyroidism on serum lipid profiles and obesity. In most reports, the definition of the upper normal limit of serum thyroid stimulation hormone (TSH) of 4.0${sim}$5.0mU/L has been used to diagnose. However, recent studies have suggested a much lower TSH cut off with an upper limit of 2.5mU/L, because >95% of rigorously screened normal euthyroid volunteers had serum TSH values between 0.4 and 2.5mU/L. Therefore we defined subclinical hypothyroidism as a TSH level greater than 2.5mU/L. We sought to evaluate the correlations of subclinical hypothyroidism with obesity index and serum lipid profiles Methods: TSH levels were measured in 6190 men and 4223 women that participated in health examination and free T4, lipid profiles (total-cholesterol, triglyceride, LDL-C), and obesity index (body mass index, body fat, waist circumference, C-reactive protein) were also measured. Results: There were significant differences of triglyceride between subclinical hypothyroidism men and normal control subjects. In women, there were also significant differences of triglyceride and LDL-C between subclinical hypothyroidism and normal control subjects. Subclinical hypothyroidism women showed significant correlations of TSH with total cholesterol, LDL-C, triglyceride, and C-reactive protein. Subclinical hypothyroidism men and women with a TSH level 2.5${sim}$4.0mU/L had significant differences of triglyceride and body fat. In men, there were significant differences of waist circumference andC-reactive protein. In women, there were significant differences of LDL-C. Conclusions: We have demonstrated correlations of subclinical hypothyroidism with serum lipid profiles and obesity index. These findings suggested that subclinical hypothyroidism people had an increased risk of dyslipidemia and obesity. Subclinical hypothyroidism people with a TSH level 2.5${sim}$4.0mU/L may be also considered suspect since it may signal a case of evolving thyroid underactivity eligible to be prevented.