BACKGROUND Subclinical hypothyroidism (SCH) is a common endocrine disorder, probably increasing cardiovascular (CV) risk. However, the relation between SCH and atherosclerosis risk factors remains unclear. OBJECTIVE The aim of the study was to evaluate selected atherosclerosis risk factors in women with SCH in comparison to a group of healthy women and women with overt hypothyroidism, as well as to investigate the influence of L-thyroxine replacement on those risk factors. METHODS The study group consisted of 187 obese women aged between 50 and 70 years: 100 women with SCH, 45 women with overt hypothyroidism and 42 women with TSH level in reference ranges. Anthropometric parameters were evaluated. Laboratory tests included thyroid hormones concentrations, lipid profile with apolipoproteins, CRP, homocysteine. Atherosclerotic indexes were calculated: LDL C/HDL C ratio, apoA1/apoB ratio and Castelli risk index. Women with hypothyroidism were given L-thyroxine treatment and after 6 months in euthyroidism the evaluation was repeated. RESULTS Total cholesterol, LDL-cholesterol and triglycerides concentrations as well as LDL-C/HDL-C ratio and Castelli index were higher in SCH than in controls and decreased after L-thyroxin substitution. All of the calculated atherosclerosis indexes showed significant positive correlations with TSH concentration in SCH group. Also in this group the systolic and diastolic blood pressure decreased significantly after treatment. CONCLUSIONS Dyslipidemia in obese SCH women is not severe, but if untreated for many years, it may lead to atherosclerosis. Substitution therapy improves the lipid profile, changing the relations between protective and proatherogenic fractions of serum lipids, and optimises blood pressure.