Nutcracker syndrome is a condition in which the left renal vein is compressed between the abdominal aorta and the superior mesenteric artery, which leads to increased pressure in the left renal vein and possible collateral veins. Clinically, Nutcracker syndrome is characterized by intermittent hematuria with or without left low back or abdominal pain. The syndrome occurs in relatively thin patients, and in adolescents who tend to be otherwise healthy. The actual incidence of Nutcracker syndrome remains unknown. Nutcracker syndrome can have a variety of clinical manifestations. The most common presentation is hematuria. On cystoscopy, hematuria flowing from the left ureteral orifice without any detectable urethral abnormality should alert for Nutcracker syndrome. Nutcracker syndrome can also cause mild to moderate proteinuria. Other manifestations are rare and include gonadal vein syndrome and varicocele. Significant collateral vessels may occur, and the gonadal, lumbar ascending, adrenal, periureteral, and renal capsule veins are all major potential collateral veins that occur as a result of compression or obstruction of the left renal vein. The mechanism for producing hematuria is thought to be due to elevated pressure in the left renal vein, resulting in rupture of a small vein into the collecting system or between the dilated venous sinus and the adjacent calyces. When evaluating hematuria, Nutcracker syndrome should have a place in the differential diagnosis when all other etiologies have been ruled out. The normal width of the abdominal aorta-mesenteric artery distance averages between 4 and 5 mm. The normal wide abdominal aorta-mesenteric artery pinch angle is maintained by the retroperitoneal fat and the third part of the duodenum. Narrow abdominal aorta-mesenteric artery entrapment angle results in entrapment or compression of the left renal vein. One hypothesis for the narrowed abdominal aorta-mesenteric artery angle is a lean body size and a decrease in retroperitoneal and mesenteric fat. Other etiologic hypotheses for nutcracker syndrome include posterior renal prolapse resulting in stretching of the left renal vein in front of the aorta and anomalous branches of the superior mesenteric artery emanating from the aorta. How to obtain a reliable diagnosis of Nutcracker syndrome remains controversial. Renal venography combined with pressure gradient measurements between the left renal vein and the inferior vena cava is the gold standard for demonstrating renal venous hypertension, although it is invasive and uncomfortable for the patient. However, there is no clear agreement on the pressure gradient threshold at which Nutcracker syndrome can be definitively diagnosed. The anteroposterior (AP) diameter and peak flow velocity of the left renal vein measured by Doppler ultrasound are helpful in the diagnosis of Nutcracker syndrome. Another study showed that correlation of renal vein inferior vena cava pressure gradient with collateral vessel flow patterns on color Doppler ultrasound would be very helpful in the evaluation of Nutcracker syndrome. CT and CT angiography are other noninvasive modalities that can show compression of the left renal vein at the abdominal aorta-mesenteric artery pinch angle as well as collateral veins. However, unlike Doppler ultrasound, the flow characteristics of the collateral vessels cannot be made. Magnetic resonance imaging (MRI) and MR angiography can also show compression of the left renal vein between the superior mesenteric artery and the aorta. Venous pyelograms and retrograde pyelograms are often normal. The most common abnormal finding is indentation of the ureter or renal pelvis due to exogenous compression of the collateral vessels. A confounding factor is that dilated left renal vein is a normal variant that can have no collateral veins and a normal pressure gradient. In patients with critical left renal vein hypertension, it is difficult to distinguish whether left renal vein dilatation is a normal variant or an early manifestation of Nutcracker syndrome. The treatment of Nutcracker syndrome is controversial. For mild hematuria, conservative management with routine urinalysis is recommended, as the development of collateral veins may resolve left renal vein hypertension and relieve symptoms. Indications for surgery include severe persistent or recurrent hematuria causing anemia and blood clots causing abdominal or low back pain. Surgical options include nephrectomy, varicose vein ligation, renal fixation, and renal vein reimplantation in the inferior vena cava. More recently, endovascular treatment options have also been used.