Lactic acidosis is the most common metabolic acidosis. At clinical presentation, several causes usually can be identified. The liver is a major site of removal of lactate and hydrogen ions, and abnormalities in the aerobic metabolism of lactate by mitochondria in hepatocytes and other cells may contribute to many clinical conditions in which overproduction and underuse of lactate occur. To date, no therapy specifically designed to lower arterial blood lactate levels has reduced mortality significantly. Prompt recognition and treatment of the underlying causes of lactic acidosis remain the cornerstone of treatment.