Emphysematous pyelonephritis (EPN) is a severe, necrotizing renal parenchymal infection that is characterized by the production of intraparenchymal gas. EPN predominantly affects female diabetics, and can occur in insulin-dependent and non-insulin-dependent patients in the absence of ureteric obstruction. Nondiabetic patients can also develop EPN, but often have ureteric obstruction and do not seem to develop such extensive disease. One gaseous component-carbon dioxide-is generated by bacterial fermentation of glucose (present in excess in diabetics) and acids. Patients with EPN show relatively vague symptoms initially, but frequently undergo a sudden deterioration in their condition, necessitating urgent medical attention. Treatment of patients with EPN comprises resuscitation, correction of any electrolyte and glucose problems, and administration of antibiotics targeting Gram-negative bacteria. Ureteric obstruction, if present, is relieved by a percutaneous nephrostomy or stent. Definitive management is by percutaneous drainage, except when there is extensive diffuse gas with renal destruction; in this case, a nephrectomy is advised. The requirement for a nephrectomy could potentially be avoided by early diagnosis and treatment of diabetics with urinary infection. With the advent of CT, a staging system of the gas patterns generated in the kidneys of EPN patients has evolved. Risk factors have been defined to aid management.