Hypothyroidism is one of the common causes of the secondary hypercholesterolemia. The prevalence of hypothyroidism in the general population is estimated to be as high as about 1.5%. Frequency of the hypothyroidism in patients with hyperlipidemia is high, and can be observed in 4.2-10% in different populations. Most commonly, there is no need to treat the hypothyroid patients with the hypolipidemic drugs. Substitution treatment with the thyroid hormones usually results in either normalization or significant decreasing of the lipid levels. Hypothyroidism with symptoms of involvement of skeletal muscles is referred as to hypothyroid myopathy in English literature, and can be present in 30-80% patients with deficiency of the thyroid hormones. Hypothyroidism is a risk factor of developing of toxic injury of muscles, what is thought to be related to hypolipidemic drug intake. We report a case of a patient with undiagnosed hypothyroidism with muscle involvement manifestation, who was treated with fenofibrate due to accidentally diagnosed hypercholesterolemia. Hypolipidemic management resulted in rapid exacerbation of previously moderate myopathy. High concentrations of muscle enzymes and moderate increasing of creatinine concentration were detected. Improvement was observed after discontinuation of fenofibrate administration, but muscle symptoms and elevation of muscle enzymes and creatinine persisted. After administration of levothyroxin, muscle weakness and laboratory abnormalities were observed no longer. After several months of follow-up we believe that treatment with fenofibrate in our patient was complicated with muscle tissue damage and exacerbated symptoms of myopathy originally related to decompensated hypothyroidism.