Hypoperfusion is the most common cause of lactic acidosis and hyperlactacidemia may be the only marker of tissue hypoperfusion.1 Suspect lactic acidosis when unexplained anion gap metabolic acidosis is encountered, especially if azotemia or ketoacidosis are not present. Evaluate metabolic acidosis, regional or diffuse tissue hypoperfusion, hypoxia, shock,2 congestive heart failure, dehydration, complicated postoperative state, ketoacidosis or nonketotic acidosis in diabetes mellitus, patients with infections, inflammatory states, postictal state, certain myopathies, acute leukemia and other neoplasia, enzyme defects, glycogen storage disease (type I), thiamine deficiency, and hepatic failure. A spontaneous form of lactic acidosis occurs. It is a prognostic index in particular clinical settings, especially in critically ill patients in shock.3 A relationship to renal disease also exists. With skin rash, seizures, alopecia, ataxia, keratoconjunctivitis, and lactic acidosis in children, consider defective biotin metabolism.4 Phenformin, ethanol, methanol, and salicylate poisoning and ethylene glycol may cause lactic acidosis. Acetaminophen toxicity causes lactic acidosis, sometimes with hypoglycemia. Cyanide, isoniazid, and propylene glycol are among the causes of lactic acidosis.1 Lactic acidosis may be due to inborn errors of metabolism.