A 57-year-old male patient was admitted to the hospital because of macroscopic hematuria. He was diagnosed as transitional cell carcinoma of the bladder. A transurethral resection of the tumor was followed by a radical cystoprostatectomy. Two months post-operatively, he was admitted to the hospital because of severe lumbar and leg pain and on the radiologic evaluation bone, right suprarenal, lung metastases and multiple abdominal lymphadenopathies were found. Meanwhile, a hyponatremia was observed and was corrected with water restriction. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) was diagnosed in the absence of other causes of hyponatremia [Turk J Cancer 2007;37(2):69-71]