CA 19-9 is a widely used tumor marker. However, an elevation in serum CA 19-9 can occur in some patients with benign disorders such as cholecystolithiasis in the absence of tumor. We treated a case of acquired ureteral stone-induced giant hydronephrosis with markedly elevated serum CA 19-9 values. After nephrectomy, the serum CA 19-9 level returned to normal. No malignant cells were found in the tissues of the resected kidney. Localization of CA 19-9 was confirmed by immunohistochemical staining of the renal pelvic mucosa. A detailed case report is presented with a review of the literature.