A 77-year-old woman was admitted to our hospital because of pneumonia and heart failure in July 2002. She had been diagnosed as having with Sézary syndrome in 1993, and had been treated with a combination of prednisolone, methotrexate, and cyclosporin A with subsequent stable disease but persistent generalized erythroderma. On admission, the white blood count was 23.9 X 10(9)/L with 28% Sézary cells, and serum creatinine levels were within normal limits. One month after admission, the pneumonia and heart failure improved remarkably with antibiotics and diuretics. However, at the same time, her renal function deteriorated with increasingly high serum creatinine levels. She died of anuria in September, 2002. An autopsy showed marked perivascular and peritubular infiltration of abnormal lymphocytes with degenerative nephrotubuli in the kidneys. This patient may be the first reported case of Sézary syndrome with renal failure caused by leukemic infiltration.