Hereditary Tyrosinaemia type I (Try I) or hepatorrenal type is an autosomic recessive trait due to a deficiency of fumarilacetoacetato hidrolase enzyme (FAH). Symptoms are variable: severe liver failure, cirrhosis, hepatocellular carcinoma, Fanconi syndrome, and peripheral neuropathy with muscle weakness. Diagnosis is confirmed by increased tyrosine (Try) serum levels and large amounts of succinylacetone (SA) in urine. Try I has a poor response to Try and phenylalanine dietary restriction. Liver transplantation is an alternative treatment. Recently a new drug, NTBC, has proved effective as treatment and eventually may become the treatment of choice for Try I. We report here our first case with Try I treated with NTBC (2(2-nitro-4-triflurormetilbenozil)-1-3-ciclohexanedione). Case: S.L.A. a 13 month old girl. His parents are healthy and no consanguineous. They have two healthy children (11 and 9 years old, respectively) and other son died undernourished, at 22 months of age, from liver and renal failure. S.L.A. was born in a city in the South of Chile, by normal delivery. Since the first months of life she presented with severe liver failure, Try was diagnosed by demonstration of SA in urine (32 umol/L; Normal value = < 0.1 umol/L) and high serum Try levels (355 umol/L). She started on a special diet with protein 2.9g prot/wt/day, calories 133 kcal/wt/day, phenylalanine 50 mg/wt/day and methionine 25 mg/wt/day. She receives 1 mg NTBC/Kg/day since 8 months of age. Currently she has normal liver function and normal psychomotor development. Her weight and height are between percentil 25-50 (NCHS). We conclude that the treatment with NTBC and special diet improved clinical symptomatology and avoided severe liver damage.