We report the case of a 68-year-old Japanese man who presented with postrenal azotemia due to bilateral upper ureteral stenosis. The patient's right kidney was nonfunctional; therefore, right nephroureterectomy was performed for the purpose of pathologic diagnosis. Histopathologic examination revealed follicular lymphoma with diffuse change in the ureter. With chemotherapy for malignant lymphoma, the stenosis of the left ureter was alleviated, and left renal function was preserved. Primary malignant lymphoma of the ureter is extremely rare. In cases of ureteral stenosis with ureteral wall thickening for which the cause is uncertain, the possibility of malignant lymphoma of the ureter should be considered.