Abstract
A 21-year-old woman was referred to our hospital because of proteinuria and hematuria. She had occasional flank pain. A renal biopsy was performed and revealed a thin basement membrane. Therefore, she was diagnosed with thin basement membrane disease. However, the frequency of her flank pain increased. Since her left kidney was slightly larger than the right, nutcracker syndrome (NCS) was suspected. Renal vein ultrasonography and venography were performed, and NCS was confirmed. Her hematuria was multifactorial, and NCS can go unnoticed if there is a comorbidity that also causes hematuria.