CLINICAL FOLLOW UP OF CHILEAN PATIENTS WITH TYROSINEMIA TYPE 1 TREATED WITH 2-(2-NITRO-4-TRIFLUOROMETHYLBENZOYL)-1,3-CICLOHEXANEDIONE (NTBC).Background: Tyrosinemia Type I is an inborn error of metabolism due to deficiency of fumarilacetoacetase. Acute presentation is with liver failure, hypophosphatemic rickets and peripheral neuropathy. Chronic presentation is with visceromegaly and subclinical rickets. The most severe complications are hepatic cancer and acute neurological crises. Without treatment, type 1 tyrosinemia is fatal. In 1992 treatment for type 1 tyrosinemia with 2-(2-nitro-4-trifluoromethybenzoyl)-1,3-ciclohexanedione (NTBC) was proposed. A clinical response was reported in 90% of patients. In cases that did not respond, a successful liver transplantation was performed, reducing mortality to 5%. Aim: To report the follow up of 12 patients treated with NTBC. Patients and Methods: Review of clinical records of  12 Chilean cases treated with NTBC at the Instituto de Nutrición y Tecnología de los Alimentos (INTA) from January 2004 until June 2010. Results: In all patients, a rapid metabolic control was achieved. Two patients developed hepatocarcinoma. One of these patients died and one was successfully treated with liver transplantation. One patient  died after receiving a liver transplantation. Nine patients have at present good liver function, but 2 had peripheral neuropathy due to late diagnosis and discontinuing NTBC treatment. Conclusions: Treatment with NTBC allows metabolic normalization in type 1 tyrosinemia, prevents liver cirrhosis and hepatic cancer, improving survival rates and quality of life in the patients. Neonatal screening is essential for the early diagnosis of this treatable disease, that otherwise can be lethal.