Hepatorenal syndrome (HRS) is a “functional” type of acute kidney injury (AKI) in patients who have portal hypertension, usually due to cirrhosis. HRS may also be caused by other liver diseases which are associated with portal hypertension, which causes decreased systemic arterial blood volume and activation of neurohormonal mechanisms, including the renin-angiotensin-aldosterone system. The resulting vasoconstriction and reduced renal perfusion trigger the release of vasodilatory substances like nitric oxide, which induces splanchnic arterial vasodilatation, leading to a decrease in systemic vascular resistance and effective circulating volume, thereby exacerbating renal hypoperfusion. HRS is a diagnosis of exclusion, and is associated with a poor prognosis. Without treatment, most patients die within weeks of the onset of AKI. Patients typically present with a progressive rise in serum creatinine, a benign urine sediment, no (or minimal) proteinuria, and a low urine sodium concentration. Ascites is often present, and severe cases are associated with oliguria. Treatment is aimed at improving liver function, if possible. Medical therapy includes increasing the systemic blood pressure with norepinephrine and albumin infusions, and administering agents that cause splanchnic vasoconstriction (e.g., terlipressin). Transjugular intrahepatic portosystemic shunt (TIPS) may be successful, and dialysis is a temporizing solution while waiting for liver transplant. The prognosis of patients with HRS is highly dependent upon reversal of the hepatic failure, whether spontaneous, following medical therapy, or following transplantation.