Nutcracker phenomenon (NCP) occurs when the left renal vein (LRV) is compressed excessively between the abdominal aorta (AA) and the superior mesenteric artery (SMA). It is called nutcracker syndrome (NCS) when NCP is accompanied by otherwise unexplainable symptoms or signs. NCS is known to be rare and has been registered as a rare condition on some medical websites, but our consecutive Doppler ultrasound data showed the prevalence of NCP and NCS of approximately 30% and 15%, respectively. There are three patterns of NCP: classical compression between the AA and SMA (type 1), compression of the LRV posteriorly by the origin of the right renal artery (type 2), and narrowed and stretched LRV anterior to the AA (type 3). The five most common symptoms or signs in NCS patients are hematuria, proteinuria, flank pain, bladder symptoms, and fluctuating glomerular filtration rate. If the diagnosis of NCS is made properly, most NCS patients may be managed conservatively without unnecessary workups. If the diagnosis is not made well, patients may worry seriously about their condition and wander from hospital to hospital. Not rarely, NCS patients are misdiagnosed as having more severe diseases, and unnecessary procedures may be done without improvement of their symptoms.