The changes of serum lipids concentrations in 15 patients with primary hypothyroidism were studied. 9 euthyroid persons in the similar age group with patients were selected as a control group. The serum levels of total and LDL cholesterol, TG, ApoAI, ApoB and ApoCII in patients before treatment were all higher than those of the control group. They decreased to normal level after treatment. The mean values of total cholesterol decreased from 6.7 mmol/L to 4.1 mmol/L, TG decreased from 2.5 mmol/L to 1.0 mmol/L, LDI-ch from 3.9 mmol/L to 2.4 mmol/L, ApoAI from 1.9 g/L, to 1.3g/L, ApoB from 1.2 g/L to 0.7 g/L and ApoCII decreased from 6.9 mg/dl to 3.9 mg/dl. There were no differences of HDI-ch level between patients before treatment and normal controls, HDI-ch level of patients only slightly decreased after treatment. Soon after the thyroid hormone treatment, all parameters of serum lipids, not including HDI-ch, were improved, as TT, level became normal, although the levels of TT4 was still not reached to normal level.