Case: A 32-year old woman was admitted to the hospital due to intractable hypothyroidism refractory to high dose of oral L-thyroxine therapy. She underwent total thyroidectomy and radioactive iodine therapy due to papillary thyroid cancer. After excluding poor adherence to therapy and malabsorption, levothyroxine absorption test was performed. No response was detected. Transient neurologic symptoms developed during the test. She developed 3 attacks consisting of neurologic symptoms during high dose administration. The patient was considered a case of isolated L-thyroxine malabsorption. She became euthyroid after intramuscular twice weekly L-thyroxine therapy.