Emergencies in nephrology are mainly acute life-threatening situations for patients. Furthermore, one needs to consider constellations that are so damaging to the kidneys that the need for permanent dialysis develops within a short period of time. Acute kidney failure as an immediate consequence is categorized using the Acute Kidney Injury Network (AKIN) stages and is pathophysiologically subdivided into pre-, intra- and post-renal. This leads to changes in volume status, acid base and electrolytes, while the terms nephrotic and nephritic describe the amount of kidney damage and help to choose diagnostic steps wisely. Patients that are already undergoing dialysis treatment or have received a kidney transplant are a further specific group in the case of emergencies.