Serum lipid levels and the roentgenograms of the Achilles' tendon were examined in ten patients with Werner's syndrome. Seven of these ten patients showed serum total cholesterol levels of more than 250 mg/dl and six of the seven patients had thickened Achilles' tendons of more than 9 mm. Significant positive correlation was found between serum levels of total cholesterol and the thickness of the Achilles' tendon in these ten patients, suggesting that substance(s) precipitated in the thickened tendon may have been derived from serum cholesterol. Moreover, some relatives suffered from hypercholesterolemia in three of the six patients with thickened Achilles' tendons, suggesting that at least these three patients may also suffer from familial hypercholesterolemia (FH). Because of this surprisingly high frequency of concurrence of Werner's syndrome and FH (three to six out of ten patients), it is possible that an abnormal lipid metabolism similar to FH may be due to some intrinsic abnormality of patients with Werner's syndrome.