Patient 1, a 26-year-old woman, had experienced a low-grade fever and abdominal pain for 1 month prior to admission. Macrohematuria also appeared 10 days before admission. She had no recent abdominal trauma. On admission, her body temperature was 37.5 C. No significant physical findings were observed in her chest and abdomen. Bilateral knocking dullness at a cost-vertebral angle was shown. The other examination was not significant, including skin lesions, lymphadenopathy, neurological findings and gynecological investigation. Urinalysis showed 0.2 g/day of protein and microscopic hematuria of 50-100 of RBCs/HPF with RBC deformity and RBC casts. A complete blood count in the peripheral blood revealed a white blood cell count of 10,800/mul. The laboratory data were as follows: serum urea nitrogen 13 mg/dl, and sCr 1.15 mg/dl. A chest X-ray did not show any abnormal findings. Meanwhile, an abdominal ultrasonography revealed bilateral hydronephrosis. An MRI study revealed bilateral hydronephrosis with focal stenosis of the right ureter at the pelvic-ureteral junction (fig. 1). Radiologists excluded retroperitoneal fibrosis, a tumor invasion and infection around the ureters, or prominent pelvic lesions. Retrograde pyelography and intravenous pyelography revealed a complete obstruction of the right ureter and an advanced constriction of the left ureter. Bacteriological examinations, including Mycobacterium tuberculosis in blood and urine, were negative. On the 9th hospital day, a stent graft was inserted in each ureter, leading to a complete improvement of the hydronephrosis. Nevertheless, the patient experienced a progressive renal dysfunction and deterioration in macrohematuria. Her sCr increased to 3.4 mg/dl, and her anti-GBM antibody count was 69 EU (normal value <10 EU) on the 21st hospital day. An open renal biopsy of the left kidney on the 25th hospital day revealed the presence of anti-GBM GN. Renal biopsy specimens revealed over 90% of glomeruli presenting with exuberant circumferential cellular crescents and the compression of the underlying tuft (fig. 2a). Immunofluorescent findings revealed intense and diffuse linear deposits of IgG and C3 (data not shown) along with GBM (fig. 2b). Her sCr and anti-GBM antibodies had worsened to 3.80 mg/dl and 112 EU, respectively, by the 26th hospital day. A plasma exchange and steroid pulse therapy followed by oral steroid treatment were administered, starting on the 28th hospital day. The patient's sCr and anti-GBM antibodies had decreased to 2.2 mg/dl and 28 EU by the 42nd hospital day. By the 80th hospital day, her anti-GBM antibodies had returned to normal, with a titer of <10 EU, and her sCr level had decreased to 1.7 mg/dl. The stenotic lesion of the right ureter was biopsied to investigate the cause of hydronephrosis. However, we were not able to determine the cause of her hydronephrosis.