Lactic acidosis is a metabolic disturbance characterized by an increase of the production/clearance ratio of lactate. Lactate is a catabolite of glycolysis when this takes place under anaerobic conditions. Clinically LA is characterized by: signs of acidosis, venous blood lactate greater than 5 mMol/l, arterial pH less than 7.25. LA is classified in type A, due to shock, and type B which, in turn, can be divided according to its pathogenesis in B1 correlated to particular pathologies, B2 due to exogenous substances and B3 caused by congenital metabolic diseases. LA is of particular interest in type II diabetes mellitus treated by phenformin. Current therapeutic directions, although suboptimal, are: to eliminate the causes of lactate hyperproduction by maintaining a sufficient efficiency of the cardio-vascular apparatus, to correct acidosis by using alkalinizing solutions, to remove pharmacologically or by dialysis the excess of lactate.