Different definitions of acute renal failure (ARF) abound. The existence of multiple definitions makes it difficult to determine the true epidemiological characteristics of this condition. Despite this difficulty, it has been possible to detect notable variations in the epidemiology of ARF during the past few decades. The absolute incidence of ARF has increased, while associated mortality rate has remained relatively static. Several factors have contributed to this altered epidemiology. Here, we discuss the relative contribution of these factors, which include site of disease onset (developed or developing countries, community or hospital or intensive care unit), patient age, infections (HIV, malaria, leptospirosis and hantavirus), concomitant illnesses (cardiopulmonary failure, hemato-oncological disease), and interventions (hematopoietic progenitor cell and solid organ transplantation).