A 10-year-old girl manifested unexplained muscle aches and high creatine phosphokinase (CPK) concentrations attributed to rhabdomyolysis in association with severe hypothyroidism due to autoimmune thyroiditis. The response to therapy strongly suggested that hypothyroidism was the cause of rhabdomyolysis. Hypothyroidism is a rare cause of rhabdomyolysis. It should always be considered in a patient with muscular symptoms and elevated CPK concentrations. In addition, the patient developed other uncommon manifestations of hypothyroidism such as pericardial effusion, acute renal failure, and acquired von Willebrand disease. After thyroxine replacement, the symptoms and abnormal findings disappeared. The patient was also diagnosed as having celiac disease, which is often associated with autoimmune thyroiditis. Conditions accompanying autoimmune thyroid disease may result from altered thyroid function and from the presence of other autoimmune diseases. The butterfly-shaped thyroid gland has a tremendous impact on metabolism, which may be compared to a phenomenon termed the "Butterfly Effect".