BACKGROUND: Familial hypercholesterolemia(FH) is an autosomal dominant inharited disorder. Total cholesterl level of FH heterozygotes is two to fourfold higher than that of normal population. Substained hypercholesterolemia results in cholesterol deposition on various organs or tissues and Achilles tendon xanthoma due to cholesterol deposition is one of the specific clinical findings of FH. One of the lipid lowering drugs, 3-hydroxy-3-methylglutaryl coenzyme A(HMG Co-A) reductase inhibitor effectively lowers the blood cholesterol level in patients with FH, but whether the cholesterol deposition can be regressed by the lipid lowering drugs is rarely reported. This study attemted to determine whether the tendon xanthoma can be regressed by lipid lowering drugs commonly used in patients with FH. METHODS: We analyzed procepectively the serum lipid levels of patients with heterozygous FH before and after lipid lowering therapy with HMG Co-A reductase inhibitor alone(Lovastatin or Pravastatin) or in combination with bile acid sequestrating resin(Cholestyramine). The Achilles tendon thickness was measured radiographically by using soft tissue technique. RESULT: Total 18 patients with heterozygotes FH(M : F=8 :10, mean age; 51.7+/-9.0 years) were treated with the HMG Co-A reductase inhibitor alone or combined with bile acid sequestrating resin and followed for mean 31.9+/-11.9 months. During that period, serum total cholesterol and low density lipoprotein cholesterol significantly fell from 329+/-42 mg/dl to 230+/-29 mg/dl and from 246+/-56 mg/dl to 151+/-28 mg/dl, respectively(p<0.001). Serum high density lipoprotein level increased and maintained 15.3% higher than basal level(p<0.01). Achilles tendon thickness decreased significantly from 13.3+/-3.1 mm to 11.9+/-3.2 mm(p<0.001) with percent reduction of 9.8+/-10.5%(range; 3.1-36.4%). The amount of change of tendon thickness was significantly correlated only with percent reductionof LDL(p=0.029) and female sex(p0.020) on univariate analysis, but it was found to be significantly correlated only with percent reduction of LDL on multivariate analysis(r=0.514,p=0.029). CONCLUSION: Achilles tendon xanthoma can be regressed by effective lipid lowering therapy with HMG Co-A reductase inhibitor alone or with bile acid sequestrating resin in patients with heterozygous FH. the regression of tendon xanthoma is likely to be related to reduction of serum LDL.