The compression of the left renal vein, which travels between the abdominal aorta and superior mesenteric artery, causes intractable microscopic hematuria called nutcracker phenomenon, also known as left renal vein compression syndrome. The right renal vein injects directly into the inferior vena cava, while the left renal vein must penetrate through the angle formed by the abdominal aorta and superior mesenteric artery to inject into the inferior vena cava. If this angle is congenitally too small or if it is filled with enlarged lymph nodes of mesenteric fat or peritoneum, it can cause nutcracker phenomenon. The hematuria produced is usually upright hematuria, i.e. hematuria appears when the body is upright and disappears in the lying position, and is mostly seen in the thinner and taller adolescents, and is rare in those over 30 years of age. It has the characteristics of non-glomerular-derived hematuria, but a few patients can show glomerular-derived hematuria and can be combined with upright proteinuria. Patients rain well, and most hematuria will slowly improve in adulthood. The diagnosis is mainly based on CT, ultrasound, and renal venography.