Subclinical and overt hypothyroidism are relatively common disorders in the general population. Thyroid hormone is known to play a role in regulating the synthesis, metabolism, and mobilization of lipids. In patients with overt hypothyroidism there is an increase in serum total cholesterol, low-density lipoprotein (LDL) cholesterol, apolipoprotein B, lipoprotein(a) levels, and possibly triglyceride levels. The effects of subclinical hypothyroidism on serum lipid values are less clear. The preponderance of evidence suggests that total cholesterol, LDL cholesterol, and possibly triglycerides are increased in patients with subclinical hypothyroidism, whereas high-density lipoprotein (HDL) cholesterol and Lp(a) remain unchanged. Most lipid abnormalities in patients with overt hypothyroidism will resolve with thyroid hormone replacement therapy. However, clinical trials to date have not shown a beneficial effect of thyroid hormone treatment on serum lipid levels in patients with subclinical hypothyroidism. The lipid-altering effects of thyroid hormone make it an appealing target for drug development. The development of specifically targeted thyroid hormone analogues that could potentially treat hyperlipidemia without causing systemic thyrotoxicosis is currently ongoing.