Non-small cell lung cancer with syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is rare. A case of squamous bronchogenic carcinoma with SIADH is reported. A 64-year-old man was admitted with 2 cm nodule of the left lung on chest radiography. Transbronchial lung biopsy revealed the squamous cell carcinoma. His past history included hypertension and hemiparesis due to brain infarction. Serum sodium level was low (122 mEq/l) and serum osmolarity was low (271 mOsm/kgH2O). However, urine sodium level was high (82 mEg/l) and urine osmolarity was high (461 mOsm/kgH2O). Renal and adrenal function was normal. He was diagnosed with cT1N0M0 squamous bronchogenic carcinoma accompanied by SIADH. He underwent left upper lobectomy with lymph node dissection. Five months after the operation, serum sodium level returned to normal. He remains well 20 months after the operation.